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{{a|systems|{{image|grail witch|jpg|“What makes you think she’s a witch?”}}}}{{quote|
{{afreeessay|crime|Lucy Letby|{{image|grail witch|jpg|“What makes you think she’s a witch?”}}
“We’ve found a witch. May we burn her?”
__TOC__
:— ''Monty Python and the Holy Grail''}}
}}{{nlp}}
{{dsh razor quote}}
{{c|Statistics}}
====On herd minds, groupthink and narrative biases====
{{drop|L|ucy Letby is}} back in the news in 2024. On 24 May, the Court of Appeal denied her leave to appeal against her convictions. On 10 June, her retrial for the attempted murder of “Child K” began in Manchester, and on 2 July she was found guilty. On 3 July the Court of Appeal released its judgment on its dismissal of her appeal. All of this came against a backdrop wherein, on 13 May, ''New Yorker'' magazine published “{{plainlink|https://wayback-api.archive.org/web/20240000000000*/https://www.newyorker.com/magazine/2024/05/20/lucy-letby-was-found-guilty-of-killing-seven-babies-did-she-do-it|A British Nurse Was Found Guilty of Killing Seven Babies. Did she do it?}}”, a 13,000-word investigative piece questioning the safety of Letby’s original convictions.
 
The ''New Yorker'' piece is — ''was'', perhaps — loosely geo-blocked in the UK, ostensibly to avoid contempt of court pending the outcome of the retrial. But it is not hard to find online, and in any case ran unedited in the ''New Yorker''’s UK print edition, so there may be some canny “Streisand Effect” marketing at play here. That a carefully researched piece is not available, when there is so much intemperate commentary published by everyone else, raises its own questions about the practicality of ''sub judice'' rules in the age of the worldwide internet, but that is a discussion for another day.
 
Having been convicted of multiple infant murders, the general public’s view is clear: justice has been done. The sooner Letby’s name fades from the commonplace the better.
 
But look a bit closer and the picture is complicated. The physical evidence implicating Letby is all circumstantial: eyewitness evidence does little more than put Letby at the scene of the alleged incidents — a place she was contractually obliged to be. No one saw her do any of the acts of which she has been accused. The medical evidence indicating foul play is technical. The strongest parts of it — relating to insulin levels — relate to children who survived. The evidence that resonates most strongly with the public — Letby’s alleged “confessional note” in particular — is not quite what it seems. Nor is the evidence that any of the infants were the victims of foul play, by ''anyone'', overwhelming. The case for conviction ''emerges'' from a preponderance of small pieces of evidence that all seem to point in the same direction. But there is no smoking gun. The most compelling proposition seems to be Letby’s ''opportunity'': she alone was rostered on and onsite during all the alleged incidents.
 
This argument is founded on ''improbability'' — what are the odds that the one nurse who was present on all occasions did not have something to do with this unprecedented cluster of cases? That said, it does not appear that either prosecution or defence brought any statistical analysis to bear on that gut sense of improbability.
 
====A binary status====
{{drop|N|ow she is}} in prison for the whole of her life, all appeals exhausted and all pending retrials completed, just two narratives are available. The simple one: she is a serial murderer of premature infants and therefore the personification of unspeakable evil; or the unthinkable one: she is the victim of a breathtaking miscarriage of justice.
 
Serial murderers of any kind are vanishingly rare in Britain. Wikipedia lists fifty-five, since 1600. But so are miscarriages of justice. Wikipedia lists fifty-four, since 1255.
 
Both the available narratives, then, are ''highly'' improbable outcomes. They leave untouched a vast range of more likely explanations which suffer the disadvantage of providing no closure on a series of tragic events: we seek narratives that explain troubling events in the world, those that say, “well, it’s hard to say” don’t. We do not find them useful. Few of us happily occupy that indeterminate space. We tend to conclusive narratives, however unlikely.
 
What is interesting is how we are pushed by our [[Systems theory|institutions]] into shutting this individual out of that wide middle ground in which she is an ordinary kid, with pluses and minuses, virtues and failings, just like the rest of us: neither angel nor devil, who had the misfortune to be involved in these tragic events.
 
The criminal justice system forces us into an odd kind of anecdotal [[reductionism]]: it focuses on discrete, actions and pieces of evidence: what was seen and done, literally microscopic observations: levels of insulin and c-peptide; unusual skin blotching patterns and so on. We are expected to thread these atoms together and build them into a picture that renders a compelling picture at a far higher abstraction level.
 
Being pattern-matching machines, we use whatever morsels we find to build a narrative. Once we are primed with a theory, we tend to dive ''deeper'' into the details to prove our case. We strive to fit whatever remaining facts we can find to fit it. Hence, we are at risk of a kind of [[Prosecutor’s tunnel vision|tunnel vision]], when our immersion in those atomic details crowds out a wider perspective.
 
It is only later, if at all, that we might ask the “big picture” question: how plausible — how ''likely'' is it that an experienced nurse with no history of mental illness, criminality, sociopathy or familial dysfunction, let alone prior medical misadventure — could suddenly transform into a killer of such sophistication as to go undetected for eighteen months? ''Why'' would a person who had dedicated her life to the medical care of newborns — who was until then, by all accounts, very good at it — suddenly begin behaving in such a destructive and vanishingly rare way? Why, in the absence of hard evidence displacing the presumption that ''this is not what normally socialised people do'', would this be the preferred theory of the case, and not “an unsual but not remarkable cluster of accidents”?
 
==Interlude: difficult cases from down under==
Three notorious cases from the antipodes illustrate the peril of preferring the atomic prosecutor’s theory against asking those big-picture questions.
====A ring of dust around Ayers Rock====
{{drop|L|indy and Michael}} Chamberlain and their three children were camping at Ayers Rock in central Australia in August 1980.<ref>''{{plainlink|https://open.spotify.com/show/4sADNVGYAf0VnP6TqaBW3i|A Perfect Storm: The True Story of the Chamberlains}}''</ref> Michael and Lindy were with other campers around a campfire when Lindy heard a disturbance near the tent where her infant daughter Azaria was sleeping. On going to check on the baby, Lindy saw a dingo leaving the tent, which was empty. The child had vanished. Lindy immediately raised the alarm. Despite a hastily organised search of the surrounding area, Azaria was never found. Lindy surmised that the dingo must have taken the child.
 
The police never really believed Lindy Chamberlain. They thought her behaviour was odd, and documented dingo attacks on humans at the time were rare. They settled on the theory that Lindy had murdered and disposed of her baby. In 1982, Lindy Chamberlain was sensationally convicted of Azaria’s murder. The police case was that in her five-minute absence from the campfire, Lindy returned to her tent, changed into tracksuit pants, took Azaria to her car, cut her throat with some scissors, waited for Azaria to die, hid the body, cleaned the blood from everywhere except the footwell of the car, changed back out of her tracksuit pants, returned to the tent, found her son and returned to the campfire without the other campers noting anything was amiss. Many aspects of the police case were logistically and phyiscally impossible.
 
Nevertheless, Lindy Chamberlain spent three and a half years in prison. When in 1986 Azaria’s matinee jacket was found four kilometres from the campsite at the entrance to a dingo lair she was released, later pardoned and her conviction finally quashed in 1992.
 
The “blood spatter” in the footwell of the car turned out, much later, to be the standard sound deadening compound sprayed on the car during manufacture.
 
====Satanic panic in the Garden City====
{{drop|I|n 1991, Peter}} Ellis, a childcare worker at a daycare centre in New Zealand was charged with horrific child sexual abuse against children in his care.<ref>''{{plainlink|https://open.spotify.com/show/1ZHmLlciFEQ33kkSPZTtyC|Conviction: The Christchurch Civic Creche Case}}''</ref> These allegations that these preschool children were abducted from the daycare centre and subjected to bizarre rituals and outlandish acts of unthinkable cruelty and violence, assault and even amputation.
 
The prosecution relied on the children’s evidence, as extracted from them by a team of social workers who, perhaps inadvertently, used suggestive interview techniques that encouraged the children to embellish and fabricate their stories. In total, one hundred and eighteen children were interviewed. The evidence of those who insisted there was no abuse was discarded, as was the testimony of patently impossible claims. The rejected evidence might have put the credibility of the remaining allegations in context but was not put before the court. The prosecution proceeded apparently on the theory that there is no smoke without fire.
 
But none of the allegations were true.
 
In 1993 Ellis was convicted on 16 counts of child sex abuse against seven children. Ellis maintained his innocence throughout and continued to fight for his name to be cleared, but died in 2019. New Zealand Supreme Court finally quashed all remaining convictions in 2022 citing a substantial miscarriage of justice due to unbalanced evidence and contamination of the children’s evidence.
 
====Murder in the family====
{{drop|O|n the morning}} of June 20,1994 twenty-two-year-old David Bain returned from his paper round at 6:45am to find his whole family had been shot dead. <ref>''{{plainlink|https://open.spotify.com/show/3jgt4218rVMRh9OcIRu8qd|Black Hands: A Family Mass Murder}}''</ref> He did not discover this immediately: it was still midwinter dark at that hour, deep in the Southern Hemisphere. Without switching on a light David first went downstairs to put on a load of laundry. He later told police it was so dark he did not notice his father’s bloodstained clothes on the machine, and inadvertently washed them with his own, obliterating key evidence.
 
Returning upstairs, David discovered his father Robin lying in the living room beside a 22 rifle with a bullet wound in his head. Quickly thereafter he found the bodies of his mother, two sisters and youngest brother, who appeared to have put up some kind of fight before being overcome. 
 
A note typed on the family computer, apparently by David’s father Robin, said, “You were the only one who deserved to live.” David placed an agitated call to emergency services. It was recorded, and remains a part of the public record.
 
David told police his father, motivated by a troubled relationship with the family, must have murdered them all before turning the gun upon himself. 
 
Based on circumstantial evidence including bloodstains on his own clothing and spectacles, fingerprints on the murder weapon, minor bruises and abrasions consistent with a struggle with his brother, and a lack of any evidence pointing to his father, David Bain was charged with all five murders and convicted on all counts.
 
David maintained his innocence.
 
In 1996 Joe Karam, a former New Zealand rugby international, became involved after reading a newspaper article about university students raising money to fund an appeal. Karam became fascinated by the case, and was persuaded of David’s innocence. He brought significant publicity to David’s cause and championed his innocence, uncovering shortcomings, inconsistencies and oversights in the police investigation and in the handling of evidence.
 
Eventually, David’s case made it to the Privy Council where, twenty years after the original trial, the court quashed Bain’s convictions and ordered a retrial. The second jury was not persuaded of David’s guilt and he was acquitted of all charges. He remains a free man.
====Narrative biases====
{{drop|T|hese three cases}} illustrate the problem of “circumstantial evidence” cases: where there is no ''direct'' evidence of the alleged crime, one tends to start with a hypothesis and then fit whatever forensic evidence you have into it. There is a kind of [[Prosecutor’s tunnel vision|tunnel vision]] at play. This is so regardless of whether you are convinced of the defendant’s guilt or innocence.
 
All kinds of odd theories circulated owing to the Chamberlains’ unusual religious beliefs — they were Seventh Day Adventists — and nationality — they were ''New Zealanders''!  But that ''anyone'' could bring themselves to do such a thing — never mind the child’s own mother — is hard to imagine. The idea that the child’s own mother would cold-bloodedly murder her nine-week-old baby without warning is ''preposterous''. And this is before considering the practical difficulties of doing what was alleged. To even set up this as a hypothesis there must be a solid basis for believing it to be possible — if not credible eye-witness evidence, then documented psychiatric instability, a history of volatile violent temperament — or at least a compelling motivation that could overthrow the powerful human instinct in almost all people to protect vulnerable infants.
 
For this to even be in contemplation as the operating theory of the case, there must be no possible alternative explanation. But Lindy Chamberlain had provided one. A dingo snatching the child might have seemed unlikely, but even with no recorded cases, it was not half as unlikely as a mother killing her own infant with a pair of nail scissors in the footwell of a car a few dozen yards from a camp fire.
 
Likewise, for Peter Ellis to have done what he was alleged to do in the first place, regardless of the evidence, would be ''extraordinarily'' unlikely. This is hideous, cruelty that very few humans alive would be capable of. For no adults to witness anything; for no-one to notice the children go missing for hours on end, for none of the children’s supposed tortures or amputations to leave any traces at all, and for there to be a plausible alternative: ''that none of the events happened at all'': that the children, perhaps to please social workers and parents afflicted by [[Prosecutor’s tunnel vision|tunnel vision]] to believe something had happened, made them up.
 
For David Bain, on the other hand, it is a different story: there is ''no question'' his family were murdered. On Bain’s own theory of the case there were only two possible perpetrators: his father and himself. Without regard to any evidence, there was a 50% chance he was responsible. And the evidence all pointed to him: For David ''not'' to be the murderer, on his own evidence, he would have to be extremely unlucky — forgetting to turn on the light, accidentally disposing of exculpatory evidence, having incriminating yet innocent injuries that he could not explain — while his dead father, whilst in no position to have exculpated himself, showed no such evidence. The grounds for appeal focused on the possibility that each piece of evidence might have an innocent explanation. To be clear, there were procedural inadequacies in the police case and David has been acquitted at law, but as a piece of judicial procedure, the comparison between Bain’s case and those of Ellis and Chamberlain is stark.
 
Lucy Letby’s case, on its face, seems a lot more like Chamberlain’s.
==Case for the prosecution==
The case for Lucy Letby’s innocence is well-stated enough. The ''New Yorker'' piece describes the statistical problems. Peter Elston and Michael McConville’s {{plainlink|https://open.spotify.com/show/2x2kstQwsyndvK0S8OOSBZ|We need to talk about Lucy Letby}} podcast goes into great detail about the technical medical credibility of the case, and ''Tried By Stats'' {{plainlink|https://triedbystats.com/|TriedbyStats}} website is excellent. There is the risk that they are all subject to [[Prosecutor’s tunnel vision|defender’s tunnel vision]], of course, but in the main the arguments they make are clear,grounded and compelling.
 
There are a collection of equally persuaded campaigners for Letby’s guilt. There is a reddit community, a couple of journalists (Liz Hull from the mail and Judith Moritz from the BBC and notably the prosecution’s main expert witness, Dr Dewi Evans, who have made a public show of dismissing the innocence campaigners. They have, in the main, the advantage that they have been intimately involved with, or at any rate present during the duration of the trial and therefore may have a sense of aspects and informal impacts that might not be apparent to a cold read.
 
====Confirmation bias====
{{drop|“A|ngel” and “devil”}} narratives become self-fulfilling: once you’ve adopted one, you can panel-beat almost any subsequent information to suit your view.
 
The little definitive peripheral evidence there is about Lucy Letby is coloured dramatically depending on who is looking at it. For example, her social media activity. Here is BBC Panorama reporter Judith Moritz, in a piece to camera,<ref>{{Plainlink|https://www.bbc.co.uk/iplayer/episode/m001q7dl/panorama-lucy-letby-the-nurse-who-killed|''Panorama'', 18 August 2023}}</ref>:
 
{{quote|
“Sparky, full of fun, popular — she looks like the life and soul of the party in these photos. I don’t know what Britain’s most prolific child killer should look like — ''I’m pretty sure it’s not this, though''.}}
 
And then, a few moments later:
 
{{Quote|“She comes across as — mousy; a bit ''normal'' — you can’t really marry that with the enormity of what she’s been accused of.”}}
 
If — and ''only'' if — we are persuaded of her guilt, her vivacious personality and active social life ''notwithstanding that malign nature'' mark her out as a psychopath. It ''corroborates'' and ''amplifies'' her wickedness.
 
If we believe she has been wrongfully convicted ''despite'' that vivacious personality and active social life — ''what sort of serial killer is like that?'' — it only confirms and illustrates the single-mindedness with which a vicious criminal system will crush an innocent, unsuspecting spirit.
 
If we hold a neutral perspective, we see this behaviour as ''perfectly'' ''normal''. It tells us nothing: it places Lucy Letby in that ordinary space, with the rest of us, within a standard deviation of the mean. There have been very, very few serial killer nurses. We have no idea what, as a rule, they are like. This information does not help us.
 
In the language of the criminal law Lucy Letby’s social media activity has low “probative” content — it doesn’t prove anything — but high “prejudicial” value — it colours any existing preconceptions a jury might hold. A court may exclude this evidence if “its prejudicial effect is out of proportion to its probative value”.<ref>Section 126, Criminal Justice Act 2003, which (per explanatory notes) preserves the common law power for the court to exclude evidence where its prejudicial effect is out of proportion to its probative value. </ref>
 
That Lucy Letby searched online for the parents of the deceased is consistent with ''either'' breathtaking malevolence — if you take it that she ''is'' a serial killer — ''or'' affecting compassion — if you take it that she is ''not''. By itself, it is ''evidence'' of neither. We all search online for individuals we meet in real life — even people we know we probably shouldn’t: this is perfectly normal behaviour. We are curious, imperfect animals.
 
====Standpoint intersection ahoy====
{{Drop|T|his case stands}} at the intersection of at least four distinct fields of enquiry: law, medicine, statistics and ethics. They are not “[[The Structure of Scientific Revolutions|commensurate]]”: each has its own rules, customs and institutions. They do not necessarily agree.
 
In a perfect world, they would converge, but the world is not perfect. They may conflict. There will be times when the correct legal outcome is not the moral one, where the moral one does not bear out the statistics, where the statistics are at odds what we know, and so on. There are inevitable incongruities.
 
Emotions are already aggravated; the stakes are raised yet higher by the undoubted loss and grief of the families of lost infants. That grief cannot be avoided. It burdens the families whatever its cause. ''That'' the families are bereaved is not at issue: the question is ''why'': neither conviction nor acquittal necessarily delivers or denies justice for their loss. One can respect the families’ unimaginable grief and seek to ameliorate it, by arguing her case.
 
====Substance, form and process====
{{Drop|W|e must keep}} in mind these different frames of reference. There is a ''substantive'' element comprising medicinal, statistical and observational information. It is filtered through a ''formal'' framework — the legal definition of “murder” — and a ''procedural'' one: the processes and customs one must observe to reach a formal legal conclusion — the presumption of innocence, the adversarial criminal justice system, the laws of evidence, the rules of court procedure, the tactics and strategies that adversarial teams must adopt within that milieu to best present their case, and the "tribunals of law and fact” — judge and jury — who must ultimately settle the question. Neither judges nor jury are necessarily, ethicists, statisticians, physicians or metaphysicians.
 
A legal conviction, or acquittal is a highly constrained, ''artificial'' process: it has evolved over centuries to favour certainty over doubt while protecting the innocent from unjust punishment.
 
By contrast, in the “town square” there is a freer debate. Blogposts, twitter threads, podcasts, discussion forums, TV documentaries and investigative journalism address different questions with different information, looser rules of engagement and greater or less intellectual rigour.
 
The justice system is gives the accused the benefit of marginal doubt. Acquitting the occasional perpetrator is a “lesser evil” than convicting a single innocent. In the town square, the accused are afforded far less doubt.
 
====The medical misadventure cases====
{{Drop|I|ndeed, cases involving}} medical misadventure, where there is no direct evidence and only subsequently collated expert evidence as to statistics or “science” make up a fair proportion of those miscarriages of justice.<ref>The “junk science” of “forensic odontology” (comparing bite marks), blood spatter analysis and hair microscopy are a recurring case of injustice: Chris Fabricant, ''{{Plainlink|https://www.audible.co.uk/pd/B09PF98JST?|Junk Science and the American Criminal Justice System}}''.</ref> Sally Clark, Daniela Poggiali and Lucia de Berk are but three examples of convicted innocents. The last two have strikingly similar facts patterns. We should not take concerns about statistics lightly.
 
Where there is no “direct” evidence, form and procedure become all the more important.
 
In Lucy Letby’s case no direct evidence definitively links her to a single murder. It is logically possible she ''did'' commit the murders, logically possible she ''did not'', and logically possible she played a role in some or all of the deaths that may warrant criticism but not a murder conviction.
 
====Probabilities====
{{drop|I|t comes down}}, at some point, to an estimation of ''probabilities''. These inform how “sure” one can be about the proposition “defendant murdered victim”.
 
These murder cases have an unusually wide range of unknowns. In isolation , we cannot say whether there was any murder at all. The deaths could have been innocent, and they could have been culpable to some legal standard short of murder (negligence, for example), and that culpability may be someone other than Lucy Letby. As the [[Post Office Horizon IT scandal]] has illustrated, striking misadventure can emerge from the collected actions of many mediocre people, none of whom had in mind any great malice. Crowds can act with delusion and madness, just as they can with wisdom.
 
Where there are unknowns we talk in terms of ''probabilities''. What are the odds that this could happen by chance? What are the odds that the same thing could happen ''repeatedly''? For there is kind of meta-statistics at play here, too: even if the odds are fair for an individual case, an unusual repetition of cases creates its own meta-narrative. It rebuts the individual presumption.
 
Roll once and get a six, and there is no surprise. This will happen one time in six, and ''there was no more likely outcome''. Rolling a one or three is just as surprising.
 
Rolling three consecutive sixes is less probable, but still not infeasible: you would expect it to hby chance once in two hundred and sixteen sequences. If you are managing tend of thousands of sequences, you should be surprised if there are not several instances of three consecutive sixes.
 
But the odds of rolling ''fifteen'' consecutive sixes are a shade better than one in half a trillion. You should start inspecting your die. It is far, far more likely that that the die is defective. (If you manufactured a half trillion dice, would not one of them be malformed?)
 
This is the essence of the “shift pattern” evidence against Lucy Letby. Being premature neonatal infants and kept in hospital, these are children at heightened risk of “natural” death: that is why they are in hospital. The number of deaths per annum varies by year, but it is greater than zero. Let us say on average there are five infant mortalities in a year. In a given year with three 8-hour shifts in a day there are roughly 1000 shifts. The probability of an infant dying on a given shift — where we have no prior information about that infant or the persons on that shift — is therefore 5/1000 or 1/200.
 
Mathematising this, for each shift, this is the equivalent of rolling a 200-sided die where 199 sides are S (for “Safe”) and 1 is M (for “mortality”). A person working 240 shifts a year would expect to be on duty for between one and two mortalities per year.
 
A person who was on duty for all five mortalities in an average year would be the equivalent of rolling five Ms and 235 Ss in the year
 
There is much, much more chance of rolling an S than an M, but if you work two hundred shifts you would expect one M. What are the odds of rolling 6 “D”s in a row? It is straightforward to calculate: one in (200 * 200 * 200 * 200 * 200 * 200). One in 64 trillion.
 
But this is not the right calculation, because there were 178 shifts
 
 
: while each of the events on her shifts was in itself explainable, the sheer number of consecutive deaths on her shift were not.
 
Unlike in Sally Clark case, prosecution did not e
 
 
Each of these enquiries requires an answer “beyond reasonable doubt”. If a victim dies in the presence of a single person with a means and motive, such that if the death was intentional there is no other possible suspect, if there is a reasonable doubt as to the death being natural — even if it probably was not — there can be no conviction.
{{Quote|
“Once is happenstance. Twice is coincidence. Three times is enemy action.”
— Ian Fleming, ''Goldfinger'' (1959)}}
Here is where a sequence makes a difference. One such occurrence might be improbable, five occurrences extremely improbable, 500,
 
==So==
What are the percentages of serial killers with history of broken homes, physical or sexual abuse, and mental illness? What percentage are female?
 
====“God complex”====
Killing people is not evidence of a God complex. The basest criminal can take life. ''Bringing people back to life '' — that is evidence of a God complex.
==Evidence==
===Insulin “smoking gun”===
In two cases (Child F and Child L) lab tests indicating high levels of insulin without accompanying c-peptide, which is prime facie evidence of administered insulin (naturally occurring insulin is accompanied by c-peptides; artificially administered insulin is not). Insulin was not prescribed for either infant. If it was true that insulin was added without prescription this is evidence of actual human agency in these two episodes.
 
The defence team accepted the prosecution’s claim that insulin was added to parenteral nutrition bags and it was presented to the court as an agreed fact.<ref>{{plainlink|https://www.scienceontrial.com/post/criminal-justice-in-england-disagreeable-facts|Science on Trial}}</ref>
 
*'''The test in question was not reliable for factitious insulin'''. From the label:
{{quote|
“Please note that the insulin assay performed at RLUH is not suitable for the investigation of factitious hypoglycaemia. If exogenous insulin administration is suspected as the cause of hypoglycaemia, please inform the laboratory so that the sample can be referred externally for analysis.”}}
*'''The test results seem to indicate very high levels of insulin''': 4657 pmol/L is about four times a dangerously high level in an adult.<ref>There is plenty of online angst about whether the level recorded was abnormally high or ''absurdly'' high, such that such a level had never been witnessed in medical history: let’s go with abnormally high.</ref> While, yes, this is what you might expect a murderer to try to do —
*'''Both babies recovered''': You might expect premature babies registering such high insulin levels — four times a critical level for an adult<ref>See: ''Very Well Health: Hyperinsulinema (High Insulin Levels)''[https://www.verywellhealth.com/hyperinsulinemia-is-associated-with-type-2-diabetes-1087717#:~:text=Your%20insulin%20levels%20are%20considered,could%20be%20diagnosed%20with%20hyperinsulinemia. .]</ref> — might have at least caused a fuss at the hospital. But not only did the babies make a full recovery, with no record of hypoglycemic coma, but —
*'''No-one even noticed the high insulin in their tests until 2018''': That is, three years ''after'' the babies made a full recovery. If you are looking for a [[res ipsa loquitur]] about these events, can we suggest that this is as indicative of negligence in the clinical staff administering the test, or the self-professed unreliability of the tests for detecting factitious insulin.
 
=== The Texas sharpshooter ===
See the {{plainlink|https://staging.d1rk7j2m6oprqr.amplifyapp.com/|TriedbyStats}} website: Over 730 shifts, with 38 “suspects” If you self-select one
 
=== The victim’s families ===
There are unquestionable victims here: the families. If Lucy Letby wasn’t responsible then this was either an unavoidable accident, in which case, there is no closure, or there is another culpable explanation — an alternative murderer seems extremely implausible — but medical misadventure of some kind is not.
Difficult
 
=== The post-it note ===
Everyone seems to accept the notes are highly inclusive and of little evidential value.
{{Quote|“The ramblings of someone under extreme psychological pressure.”}}
 
==Resources==
====Online====
*{{plainlink|https://wayback-api.archive.org/web/20240000000000*/https://www.newyorker.com/magazine/2024/05/20/lucy-letby-was-found-guilty-of-killing-seven-babies-did-she-do-it|''That'' New Yorker Article}} (choose your own snapshot from the Wayback Machine)
*{{plainlink|https://mephitis.co/the-lucy-letby-case-may-in-time-be-the-story-of-the-century/|Mephitis - The Lucy Letby Case May In Time Be The Story Of The Century}}
*{{plainlink|https://staging.d1rk7j2m6oprqr.amplifyapp.com/|TriedbyStats}}
*{{plainlink|https://www.scienceontrial.com/post/criminal-justice-in-england-disagreeable-facts|The Insulin ‘Evidence’ in the Lucy Letby Trial. Criminal Justice in England: Disagreeable Facts}}
====Podcasts====
*{{plainlink|https://open.spotify.com/show/2x2kstQwsyndvK0S8OOSBZ|We need to talk about Lucy Letby}} (Peter Elston and Michael McConville podcast)
*{{plainlink|https://open.spotify.com/show/5EZDmxyDtMPeJ1laVDWuWd|The Trial of Lucy Letby}} (Daily Mail podcast)
===The difficult cases===
There are excellent podcasts on each of the difficult cases mentioned above.
*''{{plainlink|https://open.spotify.com/show/4sADNVGYAf0VnP6TqaBW3i|A Perfect Storm: The True Story of the Chamberlains}}''
*''{{plainlink|https://open.spotify.com/show/1ZHmLlciFEQ33kkSPZTtyC|Conviction: The Christchurch Civic Creche Case}}''
*''{{plainlink|https://open.spotify.com/show/3jgt4218rVMRh9OcIRu8qd|Black Hands: A Family Mass Murder}}''
{{Sa}}
*[[Miscarriages of justice]]
*[[Texas sharpshooter]]
*[[Prosecutor’s tunnel vision]]
{{ref}}{{nld}}

Latest revision as of 11:20, 21 September 2024

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Peasant: She looks like one.

Bedevere: Bring her forward.

A Woman with a parsnip strapped to her nose is thrust forward.

Woman: I am not a witch.

Bedevere: But you are dressed as one?

Woman: They dressed me up like this.

Woman: And this isn’t my nose! It’s a false one!

Bedevere: (To the peasants) Well?

Peasant: Well, we did do the nose. And the hat. But she is a witch.

While Sir Bedevere leads the crowd through the logical ways of telling whether she is a witch, enter King Arthur, as yet unobserved.

Bedevere: Does wood sink in water?

Peasant: No. It floats. (Pauses) Throw her into the pond!

Bedevere: (Patiently) What also floats in water?

Assorted Peasants: Bread! Apples! Very small rocks! Cider! Cherries! Gravy! Mud! Churches! Lead!

Arthur: A duck.

Everyone turns in awe and wonder to the King

Bedevere: Exactly. So, logically — ?

Peasant: (Slowly nutting it out) If ... she weighs the same as a duck ... she’s made of ... wood?

Bedevere: And, therefore?

There is a long, pregnant pause.

Peasant: A witch!

— Monty Python and the Holy Grail

Preface

This piece took a long time to write. JC is no criminal lawyer, has no particular axe to grind, and found himself constantly wondering whether he had been afflicted by his own tunnel vision. Had he too fallen into the oubliette?

Ms. Letby[1] may have committed these awful crimes, or some of them, or she may be innocent. No one, but Ms. Letby, can know for sure. That is the dilemma: how to treat such uncertainty fairly. The question is whether the criminal justice system has done so. In light of its recent performances — Andy Malkinson and the Post Office sub-postmasters refer — we should hesitate before saying, “Well, she’s had her day in court and has been convicted” as if that is really the end of it.

The case raises fascinating issues that should interest lawyers in any discipline — and informed citizens in any walk of life, for that matter. Given JC’s general aspiration to try to understand the world as a complex system that behaves, and incentivises individuals to behave, in ways we would not expect, it seems like a fair topic for conversation at least.

On herd minds, groupthink and narrative bias

Herculio: ’Tis neither malice, spite, nor virtue
Whose ledger swells, or plucks, the seedy fruits of progress —
But mainly accident.
Lest thee with surety know aught else —
Withhold thy assignations.

Triago: Pish upon thee, Nuncle. Pish!
Dost thou mean to say
Things peel this way
Through doughty misadventure?

Herculio: Peradventure —

Triago: Pish abeam!
Has thou no more to say than that?
Wouldst thou on this shaky surmise
Withhold rebuke?

Herculio: Perchance, per case, mayhap dear Triago
’Twas but a fluke?

Triago: O! This nuisant planet weighs upon my soul!

Herculio: If ’tis this and nought beside
That flies you to a vernal rage
Our fickle globe in its manifold confound’ry
Lies prettily indeed
For thy alignment.

Lucy Letby is back in the news in 2024. On 24 May, the Court of Appeal denied her leave to appeal against her convictions. On 2 July, she was found guilty on retrial for the attempted murder of “Child K”.

All of this came against a backdrop wherein, on 13 May, New Yorker magazine published Rachel Aviv’s “A British Nurse Was Found Guilty of Killing Seven Babies. Did she do it?”, a 13,000-word investigative piece questioning Ms. Letby’s original convictions. This, in turn, followed a dogged campaign by a rag-tag bunch of amateur statisticians, scientists, forensic specialists and plain old keyboard warriors who were convinced of an injustice.

Since then, the mainstream media has leapt into the fray, most expressing rising discomfort about the safety of her convictions and some — notably the Daily Mail — backing both sides of the argument, running pieces in the same week by Liz Hull, who sat through the trial and is certain that Ms. Letby is guilty, and Peter Hitchens who is, vocally, not.

Having been convicted, in two separate trials, of multiple infant murders, the public’s view is — or perhaps was — clear: justice has been done. The sooner Ms. Letby’s name fades from the commonplace the better. As media consensus evolves the received view may fragment.

For as we look closer we see the picture is complicated. The physical evidence implicating Ms. Letby is all circumstantial: eyewitness evidence does little more than put her at the scene of the alleged incidents, and this may not say very much: it was a place she was, after all, contractually obliged to be.

Nor did anyone see Ms. Letby do any of the acts of which she has been accused. The medical evidence indicating foul play is in all cases technical and in most heavily conjectural. Some of the stronger parts of it — arguments about just how strong are heated — relate to babies who survived.

The evidence that resonates most strongly with the public — in particular, the notorious “shift rota” putting Ms. Letby at the scene of every incident and her alleged “confessional note”, written some months after her arrest — is not strong at all.

Nor is the evidence that any infants were the victims of foul play at all, overwhelming. They were, after all, premature infants in an intensive care unit. If they were not at high risk of mortality, they would not have been there.

The case for conviction thus emerges from a preponderance of small pieces of evidence that all point towards Ms. Letby, but weakly. There is no smoking gun. The most compelling proposition seems to be Ms. Letby’s opportunity: she alone was rostered on and onsite during all the alleged incidents.

The circumstantial evidence of the shift rota is founded on improbability. What are the odds that the one person present at all the incidents did not have something to do with them? Neither prosecution nor defence framed the argument in terms of probabilities, and none brought any statistical analysis to bear on the question. This, as several statisticians have noted, is a pity. Especially given the criminal law’s chequered history with statistical reasoning.

A binary status

Now she is in prison for the whole of her life, all appeals exhausted[2] and all pending retrials completed, just two narratives remain. The simple one is that Ms. Letby is the personification of unspeakable evil: a serial murderer of defenceless, premature infants. The other one is that she is the victim of a breathtaking, and no less unspeakable, miscarriage of justice.

Advocates on both sides grow increasingly entrenched.

But on the very same probabilities, this is a most unlikely place for the public debate to have landed.

Serial murderers of any kind are vanishingly rare in Britain. Wikipedia lists fifty-five, since 1600. But so are miscarriages of justice. Wikipedia lists fifty-four, since 1255.

Both narratives are highly improbable. Of all the explanations we might offer for the unusual spike of incidents in 2015 and 2016, as a matter of “prior probabilities” they are the least plausible: all else being equal, it is highly unlikely there was a serial murderer at work in the Countess of Chester Hospital. But, one having been convicted, all else being equal it is highly unlikely her conviction was a miscarriage of justice. This is why tempers run high. Both positions seem untenable.

They leave untouched a wide range of more probable, but less satisfactory explanations. We like our narratives to explain the world to us. We do not find useful ones that say, “Well, we just don’t know”. We prefer conclusions, however unlikely they may be.

So our institutions persuade us to deprive Ms. Letby of that wide middle ground in which she was an ordinary person, with pluses, minuses, virtues and failings. Neither angel nor devil: she just had the misfortune to be involved, somehow — we know not how — in these tragic events.

Especially where, as here, there is no direct evidence, the criminal justice system forces us into an odd kind of anecdotal reductionism: we must focus on discrete actions and isolated pieces of highly technical evidence: literally, microscopic observations: implied levels of insulin and c-peptide; unusual skin blotching patterns and so on. We expected to thread these atoms together and be able to deduce from them a compelling picture of emergent human, moral actions.

We are pattern-matching machines. We use whatever morsels we find to build a narrative. Once we have a theory, we dive deeper into the details to prove it out. We strive to fit the remaining facts into our model. We are therefore at great risk of tunnel vision, when our immersion in those atomic details crowds out a wider perspective.

Only later, if at all, do we ask the “big picture” question: leaving aside the microscopic details how plausible is it that this was murder?

Case for the prosecution

Lucy Letby’s case, on its face, seems a lot more like Lindy Chamberlain’s than David Bain’s. It is not beyond question that none of the infants — all extremely premature and in an intensive care unit, after all — met with foul play. For each event taken separately, there is a plausible non-criminal explanation. Indeed, Ms. Letby was not immediately suspected of involvement in any of the deaths.

The case for Ms. Letby’s innocence has been well-stated enough. The New Yorker piece describes the statistical problems. Peter Elston and Michael McConville’s We need to talk about Lucy Letby podcast goes into great detail about the credibility of the technical medical case — it is not very credible — and the excellent TriedbyStats website does a tremendous job of conveying just how unintuitive the statistical implications of the evidence are.

Of course, individuals committed to the proposition that there has been a miscarriage of justice may suffer their own form of “defender’s” tunnel vision — but in the main, their arguments are clear, well-grounded and compelling.

Yet this was no kangaroo court: the British justice system is rightly a thing of international renown. Over centuries, the common law has developed principles that avoid injustice. Clearly, they are not perfect, but the presumption of innocence, the burden and standard of proof, rules of criminal procedure regulating admissible evidence, pre-trial disclosure and acceptable methods of examination and cross-examination are specifically designed to ensure fairness. Ms. Letby certainly got her day in court — ten months worth of them — and spent 14 days giving evidence during her trial, at which she was represented by a King’s Counsel who left few stones unturned.

Still, there ought to be clear, well-grounded and compelling arguments to displace the presumption that Ms. Letby was simply unlucky, implicated by circumstantial evidence but fundamentally just in the wrong place at the wrong time, and instead set her out as a demonstrable serial murderer.

We might expect tunnel-visioned innocence campaigners to overlook inconvenient facts — half of confirmation bias is blindness to what you do not want to see — but not those who are persuaded of Ms. Letby’s guilt. They must, surely, be able to articulate these “clinchers”.

A strident segment of the commentariat is persuaded of her guilt. A Reddit community of yeomen amateur investigators numbers 11,000 members and is replete with theories but brooks no sympathy.[3] Journalists who covered the trial in detail have published films, podcasts and have forthcoming books about the “Killer Nurse”.[4] The prosecution’s main expert witness, Dr. Dewi Evans, has gone to unusual lengths to dismiss the concerns of innocence campaigners whom he feels to be unfairly targeting him.

But if these people can articulate these damning facts, in their voluminous reporting to date, they haven’t, particularly well.

The timid voice of protest grows louder.

Confirmation bias

“Angel” and “devil” narratives become self-fulfilling: once you’ve adopted one, you can panel-beat almost any subsequent information to suit your view.

The little definitive peripheral evidence there is about Ms. Letby gets coloured dramatically by whomever is looking at it. For example, her social media activity. Here is BBC Panorama reporter Judith Moritz, in a piece to camera:[5]

“Sparky, full of fun, popular — she looks like the life and soul of the party in these photos. I don’t know what Britain’s most prolific child killer should look like — I’m pretty sure it’s not this, though.

And then, a few moments later:

“She comes across as — mousy; a bit normal — you can’t really marry that with the enormity of what she’s been accused of.”

If and only if we are persuaded of her guilt, should an outwardly vivacious personality and busy social life mark her out as a monster. In that case it corroborates and amplifies her wickedness.

But it cannot also be evidence of her wickedness.

For, if we are prepared to give Ms. Letby the benefit of the doubt, this is perfectly normal behaviour. It tells us nothing: it places Ms. Letby in that ordinary space, with the rest of us, within a standard deviation of the mean. There have been very, very few serial killer nurses. We have no idea what, as a rule, they are like. This information does not help us. This simply tells us that Ms. Letby is not unusual.

That Ms. Letby searched online for the parents of the deceased is consistent with either breathtaking malevolence — if you take it that she is a serial killer — or affecting compassion — if you take it that she is not. By itself, it is evidence of neither. We all search online for individuals we meet in real life — even people we know we probably shouldn’t: this is perfectly normal behaviour. We are curious, imperfect animals.

Doubt

Whatever the reason for it, where there is no direct evidence of a defendant’s foul play — of any foul play — there will always be some doubt. No one saw anything. Circumstantial evidence does not speak for itself.[6] Inference is needed. An inference — from this observation to that conclusion — is necessarily an imaginative act. There are good inferences and bad ones. The question will be whether a given inference can be justified in all the circumstances. Has the prosecution done enough to remove all reasonable doubt?

In some types of crime — burglary, say — we should expect no direct evidence: competent burglars target unmonitored environments where there are no witnesses.

But burglars, we fancy, would steer well clear of the intensive care unit in a neonatal hospital. There could hardly be a worse environment to get away with crime. Entries and exits are monitored and audited. Medicine is logged, controlled, secured and signed in and out. Medical experts conduct routine rounds and check on patients around the clock. Biochemistry is complex and its signals are delicate. There are specialists at hand with deep expertise and sophisticated machinery who can detect the merest traces of the unusual or sinister.

No direct evidence

So a lack of direct evidence is a curious feature of the “healthcare serial murder” cases. This one is no exception. No one saw anyone actually doing any harm. The circumstantial evidence tends to be consistent with, rather than indicative of, wrongdoing.[7]

Avoiding eyewitnesses and leaving no forensic evidence would require great skill, caution and planning. You would expect a malign actor to refine and perfect a technique — a modus operandi — and stick with it. You would not expect such a person to make opportunistic attacks, use multiple, unrelated methods or improvise on the spot to suit the circumstances and go completely unnoticed.

Certainly not one under active suspicion. Hospital consultants raised concerns with management about Ms. Letby as early as October 2015, seven months before she was eventually suspended. You would expect some level of elevated monitoring, even informally, after that.

Calculated or opportunistic?

Ms. Letby is alleged, variously, to have injected air intravenously and via nasogastric tube, caused blunt force trauma to internal organs without external injury (quite how is not clear), overfed, dislodged breathing tubes, poisoned with insulin, and physically attacked her victims.

Yet despite these attacks using multiple, unrelated methods and sometimes being opportunistic and improvised, Ms. Letby still left no implicating evidence.

What is more, the court turned this implausible variability on its head, describing Ms. Letby as therefore “premeditated, calculating and cunning”, using a number of different methods, thereby misleading clinicians into believing the collapses had a natural cause. [8]

Perhaps — or maybe the collapses did have a natural cause. For there is one other germane feature of an intensive care unit: its patients, by unfortunate necessity, tend to be very, very sick. They have an unusually high probability of dying. If they did not, they would not be there.

There is a benign alternative explanation for this “cunning calculatedness”, therefore: that it was nothing of the kind.

Burden of proof

The law requires criminality, not innocence, to be proven. The burden is therefore on the prosecution, and it is heavy: it must prove its case beyond reasonable doubt. This is one way the system is set up to avoid injustice.

Between prosecution and defence, then, it is not a “fair fight”: the defence has a much lower threshold to win its case. If the defence must prove anything — technically it need not, but it would be a brave defendant who did not present some alternative theory of the case — it is simply that there is some credible doubt that what the prosecution alleges is what actually happened.[9]

When a seriously ill patient dies in intensive care, even unexpectedly, and no direct evidence — or circumstantial evidence, indeed, beyond mere presence — implicates the defendant, there is credible doubt.

For each collapse at the Countess of Chester Hospital, taken in isolation, there was reasonable doubt that the victim met with foul play at all, let alone that Ms. Letby was responsible for it. We know this because pathologists originally attributed every incident for which Ms. Letby was subsequently charged to natural causes.

So, how can a series individual cases, all of which do have reasonable doubt, turn into a single collection of cases which do not?

The answer is probability.

Probability and the shift data spreadsheet

Once is happenstance. Twice is coincidence. Three times is enemy action.

—Ian Fleming, Goldfinger

It is sometimes said that Ms. Letby was “not tried by statistics”, the implication being that, because they were not argued at trial, probabilities did not influence her conviction. But this is not right: a case depending on circumstantial evidence is necessarily about probabilities. The “probative value” of circumstantial evidence is simply this: “Does this evidence make it more or less likely that an event, which no one witnessed, happened?”

Statistics are not always appropriate for assessing probabilities, especially where data are limited or collected in unusual circumstances. But the shift data are statistics. The Crown may not have framed its arguments about them that way, but they were statistical: the shift data had no probative value other than as statistics.

Now: flip a fair coin once and heads is as likely as tails. That’s “happenstance”.

Flip it twice and, while two heads are less likely, they still carry a one-in-four chance. That’s “coincidence”.

But flip it twenty-five times? There is a less than one in thirty million chance of getting twenty-five consecutive heads. If you do, it is most unlikely your coin is “fair”.[10]

The shift data seem to be like a string of twenty-five coin flips that all came up heads. If they are they can dispel those “credible doubts” that remain in individual cases: okay, each single collapse may have been as likely as not innocent. Two, a coincidence. But twenty-five?[11]

If there is a single clinching argument in the evidence presented against Ms. Letby, this was surely it.

But there are two objections to this reasoning:

Firstly, it draws a false dichotomy between “foul play” and “natural causes”.

The range of “natural causes” that could trigger a medical collapse is wide and necessarily indeterminate. The range of malicious causes of a collapse with which a defendant has been specifically charged are necessarily limited and finite.[12] It is not a “fifty-fifty” alternative. Since Q.E.D., we don’t know them all, we cannot calculate prior probabilities of an unlimited range of potential natural causes. Nor, therefore, can we calculate their inverse, which is the probability of the single malicious cause. This puts an upper bound on the prior probability of that malicious cause and ought to make arguing malice from simple probabilities very difficult.[13]

Secondly, the logic only holds if the “flips” really were consecutive.

If there were fifty flips, and only twenty-five came up heads, that would not be unusual at all.[14]

And here we come to the notorious spreadsheet setting out the shift data. It comprises a small selection taken from a much bigger sample of a thousand or more shifts in the thirteen-month “suspect period”.[15] It contains only the shifts germane to the events for which Ms. Letby was charged. Given the prosecution’s reliance on circumstantial evidence to bring charges, we can assume that “Ms. Letby being on duty for a given incident” determined whether she was charged with it. If she was not, there would not be enough evidence to dispel reasonable doubts.

That is to say, all the events on the spreadsheet necessarily occurred while Ms. Letby was on duty. The chart tells us simply that she was on duty every time she was on duty.[16]

There is some debate about whether, when they originally reviewed the hospital data, the police already had Ms. Letby in mind as a possible suspect. If they did not, it is argued, that might give more weight to this evidence. But the material point in time is not when they first reviewed the evidence but when they assembled this spreadsheet. At that point, in preparation for the trial, the prosecution certainly did have Ms. Letby in mind, so the question is moot, and in any case, could have been avoided by providing all relevant shift data to the court, rather than a conveniently filtered subset.

The spreadsheet’s use in evidence has thus been widely criticised, perhaps most eloquently by Rachel Aviv in her New Yorker article. Aviv raises the prospect of the “Texas sharpshooter” fallacy.[17] Are all the incidents included? Did any relevant events happen when Ms. Letby was not on duty? What even counts as a “relevant event”? Has inconvenient data that does not fit the prosecution narrative been omitted?

There were ten other deaths in the suspect period for which Ms. Letby was not charged. We do not know why she was not charged, nor whether she was on duty for these events. (A few commentators claim to have seen evidence that Ms. Letby was on duty for every death in the suspect period — but that evidence is not public, and importantly does not seem to have been presented at trial.)[18]

Had the Crown submitted a comprehensive table including every shift in the suspect period, and marked every incident on it, whether Ms. Letby was implicated or not, we might have a better story. But they did not.

In the aftermath of Ms. Letby’s original conviction police hinted “further charges may be forthcoming” as they continued to review thousands of historical cases dating back to 2012. That was easy to say and hard to rebut. But, in the twelve months since that statement, the police have brought no further charges. Since they have now had nine years to review that evidence, it does not seem unreasonable to suppose the search has not turned anything up.[19]

On “tonewood” and prosecutor’s tunnel vision

Triago: Ho, Ho.
Let not thy witty fool, nor his foolish wit
Besmirch the fruited science of th’ academy.
“A little learning is a dangerous thing” —

Nuncle: Yet not half so dangerous as a lot.

Triago: — So sayeth Pope, you know.

Nuncle: But not the one in Rome:

Queen: Good ser knight: art thou drunk upon the Pierian spring:
A hypoxic draft that suffocates the brain,
So deep no shaft of light can bring it round again?

Triago: My conjecture comports a grain of truth
As pure and true and golden—

Nuncle: — but yet no more roundly causative
Than are the month-past flappings of a Latin papillon
Upon a brewing Filipino typhoon.

—Otto Büchstein, Die Schweizer Heulsuse

JC has, elsewhere, waxed long and lyrical about the collection of cognitive biases called prosecutor’s tunnel vision. They tend to show up where clinching evidence does not: if there were any clinchers, things would be clinched. Those prosecuting — and, for that matter, defending — fixate on finer and finer technical details to win more and more isolated arguments. Once one side goes down a rabbit hole, the other is obliged to follow. Insulin assay tests, entry card swipe data, the significance of skin discolouration — all have been cited as smoking guns for prosecution and defence when they are transparently nothing of the sort.

The fact is, there are very few political, social, and especially personal problems that arise because of insufficient information. Nonetheless, as incomprehensible problems mount, as the concept of progress fades, as meaning itself becomes suspect, the Technopolist stands firm in believing that what the world needs is yet more information.[20]

—Neil Postman

Information is fractal. The more you look at it, the more you can create: it subdivides infinitely — there is no bottom — and the more raw information you create, the more possible arguments you can have about it. This is the implication of information theory: the more data points there are, the more unique patterns you can make from them.[21] If we take it that a theory is simply “a pattern of consistent data drawn from available information from which we can draw a valid inference” then the more information you have, the more plausible alternative theories of the case you can make.

In other words, you cannot win an argument by simply descending further into the weeds. Those who have drunkenly debated evangelical Christians, resolute atheists, real ale connoisseurs, or tonewood freaks — JC has done all of these — will know this. The thing about descending into the oubliette is that as the points atomise the arguments grow more heated and numerous and the less difference they can possibly make.

This is the “tone-wood” debate in a nutshell: sure, in theory the harmonic resonance of nitrocellulose varnish could affect the sound of an electric guitar, but not so as a mere human could possibly hear it in perfect conditions let alone in the moshpit at the Roxy on a sweaty night in 1976. Whatever made Steve Jones’ Les Paul sound like a screaming chainsaw, that is, it wasn’t the varnish.

Zeroing in to draw further inferences will not help. The only way to do it is by zooming out.

Oh come on, ref —

“In this case, Letby is a young, white, English nurse from a reputable, normal background. So it’s not surprising that some people respond to the fact that she has been found guilty of killing babies by saying it hasn’t happened. It becomes about shooting the messenger — which, in this case, is me.”

—Dr. Dewi Evans, prosecution expert witness, The Times, 7 July 2024

It is a common enough trajectory: we start with an instinct that a popular, diligent, young, female nurse from a stable background is the last person you would expect to be a serial murderer.

We quietly chide ourselves about our unconscious bias in favour of people like us. We remind ourselves that natural sympathy with our in-group is not scientific, let alone legal evidence. The law requires us to set that kind of pre-judgment aside and consider the evidence as it accumulates in the abstract and on its merits.

But hold on: if circumstantial evidence “changes the prior probability of an event”, it adjusts the inferences we can reasonably draw from baseline facts.

Inasmuch as Ms. Letby’s background, socialisation and mental health reflect the prior probability that she would not be a murderer, and inasmuch as they are not displaced by direct evidence that she is a murderer, then our intuitions are useful. They are all we have. If we ignore them, our pattern-making instincts may lead us down rabbit-holes, chasing down tendentious circumstantial minutiae at the expense of basic common sense.

This is how miscarriages of justice happen.

The Northern Territory Coroner’s report to Lindy Chamberlain’s trial is perhaps a high watermark of this kind of thing. Recall that Lindy Chamberlain had immediately claimed to have seen a dingo exiting Azaria’s tent. A week after her disappearance, Azaria’s torn and bloodstained jumpsuit was discovered in the desert, 4 km from the campsite. Case closed, surely?

No. Rather than seeing this as corroborating Mrs. Chamberlain’s story, the coroner arrived at precisely the opposite conclusion:

The evidence in relation to the clothing is consistent with an attempt to simulate a dingo attack on a child by person or persons who recovered the buried body, removed the clothing, damaged it by cutting, rubbed it in vegetation and deposited the clothes for later recovery. Such deposition is indicative that the deposition was made with the knowledge that dingos were in the area.

In addition, there is no evidence to positively support the involvement of a dingo in the taking of the child, the carrying of the body some four Kilometers and removing the body from the area where the clothes were found.

Prior probabilities, again: not only did Lindy Chamberlain have no opportunity to fabricate this evidence or make the eight-kilometre round trip to plant it, and not only did no one see her doing so, it was in any case vanishingly unlikely that a sane, well-adjusted and happily-married mother of three children would murder her own child in the gruesome way suggested. Without direct evidence to support the coroner’s theory, it was preposterous.

Before even entertaining the possibility of foul play, the coroner should have asked himself, and satisfactorily answered, a far simpler question: why on Earth would any normal, well-adjusted mother do that?

Now, barristers will remind us that motive is never required for a criminal conviction, and this is true. But. If there is no direct evidence of wrongdoing, there is a plausible innocent explanation and we cannot plausibly answer the question, “Why on Earth would she do that?” we should proceed very carefully.

Are we really to believe that an experienced nurse with no history of mental illness, criminality, sociopathy or familial dysfunction, let alone prior medical misadventure — could suddenly transform herself from a trusted senior medical professional into a killer of such sophistication as to go undetected for eighteen months? Even while suspected?

Are we really to believe that, when suspended from her duties as a result of management suspicion of criminal activity, a serial murderer would launch a grievance procedure to get back on the ward?[22]

How could she do this? Why would she do it? Why, in the absence of compelling, hard evidence displacing the usual presumption that this is not what normally socialised people do, would the preferred theory of the case be serial murder, and not “an unusual but not remarkable cluster of accidents”?

Miscarriages of justice and the perfect crime

Lucy Letby may be guilty. These preposterous suppositions may in fact be true. But we may still question the process. It may seem outrageous that there is such a thing as the “perfect” crime, where a villain leaves no trace and walks away scot-free, but this is the cost of ensuring the system does not lightly condemn the innocent. As a general proposition, you cannot convict someone of a crime for which there is no evidence.

Here, again, is our old friend form over substance: this time, the requirement for form following the uncomfortable implication of epistemology that we cannot know substance. Form is all we have.

Here the difference between direct and circumstantial evidence is stark. If there is reliable witness evidence that the defendant did it, or did not do it, then the standard of proof can be satisfied easily. There is not much call, or even scope, for doubt.

But where there is no direct evidence that the defendant did anything — no eyewitness testimony, no CCTV, no uncoerced confession — then our inferences from circumstantial evidence that she did do something will have to do an awful lot of work.

They must create an overwhelming probability that these were not natural causes but murders and the defendant was responsible for them.

The healthcare serial murder cases

There is another baseline probability to consider: that there has been a miscarriage of justice perpetrated against a medical professional accused of serial murder by poisoning.

Here is the scenario:

There has been an unusual increase in incidents at a hospital for which no obvious “innocent” explanation exists. One nurse was present for all the incidents, but there is no direct evidence that she actually harmed any patients. Though many pieces of weak circumstantial evidence are consistent with the nurse’s involvement, she had no apparent motive, nor any history of violence, antisocial behaviour, criminality or mental illness. The nurse steadfastly denies responsibility.

This might sound like a highly tailored set of circumstances, specific to Ms. Letby alone.

But in the last fifty years, several cases have fitted this description exactly: Jessie McTavish (Scotland, 1974), Filipina Narciso and Leonora Perez (USA, 1975), Susan Nelles (Canada, 1981), Orville Lynn Majors (USA, 1993), Jane Bolding (USA, 1998), Daisuke Mori (Japan, 1999), Vickie Dawn Jackson (USA, 2000), Colin Norris (UK, 2002), Benjamin Geen (UK, 2004), Abraão José Bueno (Brazil, 2005), Petr Zelenka (Czech Republic, 2006), Lucia de Berk (Netherlands, 2010), Rebecca Leighton (UK, 2011), Victorino Chua (UK, 2011), Daniella Poggiali (Italy, 2014) and, of course, Ms. Letby.

Of these 17 prosecutions, two (Nelles and Leighton) were abandoned before trial, five (Filipina Narciso, Leonora Perez, Bolding, De Berk and Poggiali) were convicted but then substantively[23] acquitted on retrial, and three (Geen, Norris and Letby) are the subject of active ongoing innocence campaigns.

This is not to suggest it is impossible for a nurse fitting Ms. Letby’s description to be guilty of serial murder, but that the baseline probability of a miscarriage of justice in a case like hers is surprisingly high.

To return to the initial observation: serial murders are vanishingly rare, healthcare serial murders even rarer and so, as a general rule, are miscarriages of justice.

But miscarriages of justice in healthcare serial murder cases are pretty common.

— So?

It remains to be seen whether the criminal justice system will allow any of this to be tested. Ms. Letby’s conventional avenues for appeal[2] are already exhausted. Just as the system is designed to afford defendants a fair hearing before the jury’s decision, the prerogative of certainty in the criminal justice system makes it very hard for a defendant to challenge a jury’s decision on the facts afterwards.

Failures of Ms. Letby’s defensive strategy — not calling expert witnesses, not introducing evidence that was available at the time of the trial, not challenging the misleading probabilities implied by the shift rota — are not grounds for further review. This is, yes, form over substance, but the hurdles are still formidable.

Influential commentators[24] have questioned whether the procedural rules surrounding the use of expert witnesses are fit for purpose in light of Ms. Letby’s case. There is some suggestion that key evidence[25] was misinterpreted at the original trial. This might be grounds for appeal, but it does not seem likely.

The other unknown is the forthcoming Thirlwall Inquiry into the deaths at the Countess of Chester hospital. Its terms of reference do not include relitigating Ms. Letby’s convictions, but the rising pitch of public disquiet may make their adjustment unavoidable.

We will see.

Resources

Online

There is a lot of debate online about the case, much of it acrimonious and, even when not, it descends into deep oubliettes of peripheral materiality.

JC’s observation — perhaps evidence of his own tunnel vision — is that the arguments defending Ms. Letby tend to be more analytical and less emotionally involved than those favouring conviction. The sceptical case focuses on the soundness of the statistics and the consistency and plausibility of the forensic analysis (albeit this can descend into the oubliette at times). Those supporting conviction can be more emotive and ad hominem, describing ms. Letby’s defenders as “conspiracy theorists”, “cranks”, a “diverse band of fanatics and pseudo-scientists”, and “members of the ‘butterfly’ gang” who comprise “half a dozen or so middle-aged women who wear their yellow badges with pride” and who count, er, “scientists, neo-natal nurses, doctors and statisticians” amongst their number!

Arguments for the defence
Arguments for the prosecution

Similar difficult cases

There are excellent podcasts on each of the difficult cases mentioned in our “Prosecutor’s tunnel vision” article.

See also

References

  1. ↑ JC will use the neutral honorific as a matter of courtesy. Using just her Christian name feels too familiar; her surname too brusque.
  2. ↑ 2.0 2.1 I am indebted to a reader for pointing out that there is one pending appeal, on convicted for attempted murder following the retrial.
  3. ↑ Moderators fiercely police contributions: anyone so much as questioning the verdict is summarily banished. JC was banished.
  4. ↑ Notably, Liz Hull from the Mail and Judith Moritz from the BBC.
  5. ↑ Panorama, 18 August 2023
  6. ↑ Some legal commentators, who should know better, have been publicly confused about this when discussing Ms. Letby’s case.
  7. ↑ Speculative expert evidence that, for example, “blotched, mottled skin is consistent with air embolus” is of little probative value unless it is not consistent with a more likely innocent explanation. If innocent explanations for the observation occur more frequently in the base rate than air embolus, the inference could be disproportionately prejudicial.
  8. ↑ Mr Justice Goss’s sentencing remarks include the following:

    You used a number of different ways to try to kill them, thereby misleading clinicians into believing the collapses had, or might have had a natural cause or were a consequence of a developing medical condition.  You took opportunities to harm babies when staff were on breaks or away from babies.

  9. ↑ This misunderstanding of who is required to prove what is a characteristic of the online debate. The defence is not required to prove a defendant’s innocence.
  10. ↑ This assumes that the “base rate” of “unfair coins” in a given sample of coins is greater than one in thirty million.
  11. ↑ This mischaracterises the probabilities for the sake of simplicity. In the absence of evidence implicating a defendant, the prior probability of a single collapse being “innocent” is far greater than “evens”. An “innocent” collapse includes every possible cause for a collapse other than the defendant’s foul play.
  12. ↑ The jury was instructed:

    “If you are sure that someone on the unit was deliberately harming a baby or babies, you do not have to be sure of the precise harmful act or acts.”

    Stated that bluntly, it seems to put the cart before the horse: it is hard to see how someone could be sure there was deliberate harm without being clear about how it was inflicted. A nuanced interpretation might be:

    “If you are satisfied it was “one of a range of identified actions” but you don’t know which, then that will suffice.”

    In any case, the range of potential means of harm is limited.

  13. ↑ We cannot, strictly speaking, use probabilities to predict future events in an unbounded system. A probability distribution describes the probabilities of all possible outcomes of a given random phenomenon in a given sample space. There are two components to this: the events must be random, and all possible events in the sample space must be known. This is true of a flipped coin — the sample space is {heads, tails} — but not medical outcomes in an intensive care unit. We should be very cautious about relying on probabilities in an indeterminate space. However, where events are in the past and we have no information about what caused them, we can treat them as “functionally random”. Though we cannot know all possible outcomes in the sample space, this puts an upper bound on potential probabilities, not a lower bound. For example, if we know there were at least five possible outcomes, but there may have been more, we can say the probability of the outcome that actually happened was no higher than one-fifth. This tends to argue against the likelihood of finite events in an indeterminate sample space.
  14. ↑ To be precise, not quite: there would be 49.65% chance of happening, a chatbot I know reliably informs me.
  15. ↑ The thirteen-month period between June 2015 and July 2016 in which the charges were laid. There is an argument that even this period brings an element of confirmation bias about it, and the enquiry should be extended to Ms. Letby’s entire tenure at the hospital.
  16. ↑ TriedbyStats has an excellent interactive feature to demonstrate the vanishing unlikelihood of another nurse being on duty for every one of Ms. Letby’s shifts.
  17. ↑ Having peppered the side of a barn with gunshots, a marksman finds a cluster of five bullet holes within a foot of each other. Ignoring all the other bullet holes he paints a target around them and claims to be a sharpshooter.
  18. ↑ Notably BBC Panorama: “The jury was only asked to consider seven murder charges. We’ve discovered that 13 babies died during Lucy Letby’s last year on the neonatal unit. She was on duty for every one of them.”
  19. ↑ The Scotsman, 18 August 2023.
  20. ↑ Neil Postman, Technopoly: The Surrender of Culture to Technology, 1992.
  21. ↑ Simply put, if you have one data point, you can make one possible combination. If you have two, you can make three (A, B, AB). If you have three, you can make seven (A,B, C, AB, BC, AC, ABC), and so on.
  22. ↑ There are healthcare serial murder cases where the defendant has abruptly left the workplace on suspicions being raised. This seems a much more likely course of action.
  23. ↑ Jessie McTavish was also acquitted on retrial, but on a procedural technicality.
  24. ↑ David Allen Green’s Empty City blog and MD in Private Eye
  25. ↑ Literally, “key” evidence: data taken from key-card door-swipes recording who was entering or leaving the ward.
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