Talk:Lucy Letby

Those Lucy Letby experts in full

Name	Profession	Field	Interest	Camp
Dr. Andreas Marnerides	Consultant	Pathology	Prosecution expert witness	Prosecution
Dr. Owen Arthurs	Professor	Radiology	Prosecution expert witness	Neutral
Dr. Sally Kinsey	Professor	Haematology	Prosecution expert witness	Neutral
Dr. Peter Hindmarsh	Professor	Endocrinology	Prosecution expert witness	Prosecution
Dr. Stavros Stivaros	Professor	Radiology	Prosecution expert witness	Neutral
Dr. Simon Kenney	Consultant	Paediatrics	Prosecution expert witness	Neutral
Dr. Dewi Evans	Medical Doctor	Paediatrics	Prosecution expert witness	Prosecution
Dr. Sandie Bohin	Medical Doctor	Paediatrics	Prosecution expert witness	Prosecution
Dr. Ravi Jayaram	Consultant	Paediatrics	CoCH Employee, Prosecution witness	Prosecution
Dr. Stephen Breary	Consultant	Paediatrics	CoCH Employee, Prosecution witness	Prosecution
Dr. John Gibbs	Consultant	Paediatrics	CoCH Employee, Prosection Witness	Prosecution
Dr. Shoo Lee	Professor	Neonatology	Independent	Defence
Dr. Neena Modi	Professor	Neonatology	Independent	Defence
Dr. Geoff Chase	Professor	Mechanical Engineering	Independent	Defence
Dr. Jane Hawdon	Consultant	Neonatology	Independent	Neutral
Dr. Michael Hall	Consultant	Neonatology	Defence expert witness	Defence
Dr. Roger Norwich	Consultant	Neonatology		Defence
Dr. Eric Eichenwald	Professor	Paediatrics	Independent	Defence
Dr. Helmut Hummler	Professor	Neonatology	Independent	Defence
Dr. Tetsuya Isayama	Professor	Neonatology	Independent	Defence
Dr. Joanne Langley	Professor	Paediatrics	Independent	Defence
Dr. Sandra Moore	Consultant	Neonatology	Independent	Defence
Dr. Mikael Norman	Professor	Paediatrics	Independent	Defence
Dr. Bruno Piedboeuf	Professor	Neonatology	Independent	Defence
Dr. Prakeshkumar Shah	Professor	Paediatrics	Independent	Defence
Dr. Nalini Singhal	Professor	Paediatrics	Independent	Defence
Dr. Erik Skarsgard	Professor	Paediatrics	Independent	Defence
Dr. Ann R. Stark	Professor	Paediatrics	Independent	Defence
Dr. Helen Shannon	Professor	Chemical Engineering	Independent	Defence
Dr. Christian Yates	Professor	Mathematical Biology	Independent	Defence
Dr. Alan Wayne Jones	Professor	Forensic toxicology	Independent	Defence
Dr. Peter Green	Professor	Statistics	Independent	Defence
Dr. Richard Gill	Professor	Statistics	Independent	Defence
Dr. Svilena Dimitrova	Consultant	Neonatology	Independent	Defence
Dr. Neela Shabde	Consultant	Paediatrics	Independent	Defence
Jenny Harris	Intensive Care Nurse	Neonatology	Independent	Defence
Dr. Stephen Senn	Professor	Statistics	Independent	Defence
Dr. Tariq Ali	Consultant	Paediatrics	Independent	Defence
Dr. Philip Dawid	Professor	Statistics	Independent	Defence
Dr. Jane Hutton	Professor	Statistics	Independent	Defence
Dr. Gillian Tully	Professor	Forensic Science	Independent	Defence
Dr. Neil Aiton	Consultant	Neonatology	Independent	Defence
Lord Sumption	Supreme Court Judge	Criminal Law	Independent	Defence
Dr. Faye Skelton	Professor	Criminology	Independent	Defence
Dr. Colin Morley	Professor	Neonatology	Independent	Defence
Dr. Richard Taylor	Consultant	Neonatology	Independent	Defence
Dr. Waney Squier	Consultant	Pathology	Independent	Defence
Dr. Matthew Orde	Consultant	Pathology	Independent	Defence
Dr. David Wilson	Professor	Criminology	Independent	Prosecution
Dr. Keith Frayn	Professor	Human Metabolism	Independent	Prosecution
Dr. Normal Fenton	Professor	Statistics	Independent	Defence
Dr. Scott McLachlan	Lecturer	Informatics	Independent	Defence
Dr. John Ashton	Professor	Public Health	Independent	Defence
Dr. David Livermore	Professor	Medical Microbiology	Independent	Defence
Michele Worden	Practice Nurse	Neonatology	Former CoCH Employee	Defence
Dr. John O’Quigley	Professor	Statistics	Independent	Defence
Dr. Carola Vinuesa	Professor	Immunology	Independent	Defence
Dr. Adel Ismail	Consultant	Endocrinology	Independent	Defence
Adam King	Barrister	Criminal Law	Independent	Defence
Dr. Ivan Blumenthal	Consultant	Paediatrics	Former CoCH Employee	Defence
Dr. Joseph Wolfsdorf	Professor	Hypoglycaemia	Independent	Neutral
Dr. Charles Stanley	Professor	Paediatrics	Independent	Defence
Dr. MaAhew Johll	Professor	Forensic Science	Independent	Defence
Dr. Hilde Wilkinson-Herbots	Associate Professor	Statistics	Independent	Defence
Karen Rees	Head of Nursing	Paediatrics	Former CoCH Employee	Defence

Now, true, those professing Letby’s innocence are prone to confirmation bias too. but if you looked at it probabilistically, the competing “confirmation biases” are these:

the likelihood of a healthcare serial murderer (an extremely unlikely scenario) to a very high degree of certainty (>95% confidence level)

the likelihood of a spike in neonatal deaths in a specific location with any other cause at all, to a very low degree of certainty (>5% confidence level).

Now it is true that there is more evidence than just a statistical spike: there were also specific forensic findings, documentation irregularities, and behavioural evidence that factor into the overall probability assessment. And the "reasonable doubt" standard isn’t purely mathematical — it’s about whether alternative explanations are reasonable given all available evidence, not just whether they're statistically possible.

In the absence of direct evidence, all circumstantial evidence amounts to an inference that makes the allegation more or less likely. In cases built on circumstantial evidence, what we’re doing is building a probabilistic case through multiple layers of inference. To be sure, you can’t precisely quantify it, but that is not to say it is not a question of probability. The prosecution’ compiles enough of these probability-modifying factors to cross the beyond reasonable doubt threshold, while the defence only needs to introduce enough doubt in any of these inferential chains to keep the total probability below that threshold.

This is why the “coincidence” argument is so central. The multiplication of improbable coincidences makes the innocent explanation vanishingly unlikely. But this reasoning is vulnerable to several statistical criticisms, such as the Texas sharpshooter fallacy and selection bias.

In the absence of compelling direct or even circumstantial evidence (and much of the forensic evidence has been strongly criticised) it comes down to probabilities. This is where Bayesian reasoning comes in: if you have direct evidence of actual direct harm, that changes the priors. If you don’t then really the prior probabilities are all you have.

And the absence of direct evidence over a sustained period in as heavily controlled, regulated and monitored an environment as a hospital, especially against a person who has no known expertise in serial murder and took no known steps to research methods of killing without leaving evidence, is telling in itself.

There is a kind of paradox here: the very absence of evidence over such a sustained period, in such a tightly monitored environment, against someone with no apparent expertise in committing these crimes let alone avoiding detection, becomes probative in itself. It makes the prosecution narrative require additional unlikely assumptions about extraordinary competence in evidence elimination that nothing else in the case supports.

This fits into a Bayesian framework because the probability of seeing a pattern of “no clear evidence” would be higher under “innocent” explanations — where of course there could be no such evidence — as against the murder hypothesis, where such evidence would potentially exist, so there would be a presumption that a tightly monitored environment would catch it. would expect some physical or direct evidence to emerge given the circumstances.

This is why, i think, the "letby is guilty" faction are at pains to de-escalate the importance of statistical analysis

Letby canards

The evidence wasn’t just Dr. Evans, you know

Frequently heard: You make this sound like this was based on one man’s evidence. But in fact there were many extremely expert witnesses called for the prosecution. It was not just the Dewi Evans show.

This is true, numerically — per the table of experts, there were no fewer than eight prosecution expert witnesses, and at least two consultant neonatologists who gave ordinary Crown evidence — but the numbers do not tell the whole story.

As noted elsewhere, the proving out a prosecution case is a meticulous and laborious. You must adduce evidence to prove even uncontroversial facts. And that is what has happened here: Drs. Arthurs, Kinsey, Stivaros and Kenney have provided evidence that provides a platform for the prosecution theory, without seeking to administer, let alone landing, any killer punches. Drs. Arthur, Kinsey and Stiavros each, quite properly, conceded their evidence was consistent with, but not necessarily exclusive to, the prosecution theory. There seems to be no record of Dr Kenney’s evidence at all, which I surmise means it was admitted into evidence as a written record and not thereafter discussed at all, meaning it was necessarily uncontroversial.

This leaves just four expert witnesses: Drs. Evans, Bohin Marnerides and Hindmarsh.

The defence experts don’t agree!

A correspondent writes:

What’s interesting about the ‘defence’ experts is that they don’t all agree with each other, and some have even conceded the prosecution argument is plausible - insulin poisoning is a possibility, some get evidence entirely wrong.

This is quite so. Some of the defence witnesses do concede that the prosecution case could be correct: they just think it extremely unlikely, and that there are far more plausible explanations.

When setting out a defence. there is always an element of lawyers’ style “pleading arguments in the alternative”, but here we should regard these dissonances as useful:

Firstly, you would expect truly independent experts not to fully agree. On difficult matters of scientific interpretation at the margins, there are always divergences of opinion, even amongst world leaders. And that they don’t agree rather undermines the insinuation, rather frequently made, that these experts are engaged in an elaborate conspiracy.

In any case, the defence industry is not to prove a single, unified, entirely consistent theory of the case. To the contrary, the position is “our client had nothing to do with it. We have no special insight into how these collapses happened, beyond being certain it was nothing to do with Ms. Letby.”

Rather, the defence’s job is to cast doubt on the prosecution’s single, unified theory of the case. And in doing this, throwing in non-consistent alternatives is not problematic at all. To say that the collapses could have been caused by any of clinical negligence, malpractice, surgical misadventure, pre-existing illness, hospital infection, undiagnosed hypoglycemia, etc. etc. — you name it — is to put the specific prosecution view, that these were all the actions of an unobserved malign actor — to the sword. These alternatives may indeed be inconsistent, but each has its own non-zero individual probability. Even if mutually exclusive — and most of them are not — what matters is that these alternatives are exclusive of the specific prosecution allegation. If they are, then their individual non-zero probabilities, summed up, must be subtracted from one, and the probability that the prosecution’s theory is correct cannot be greater than the remaining value. It may well be less.

It is painful/disrespectful to the victims’ families

Surely this one is true only if miscarriage campaigners are mistaken and acting in bad faith. We need to separate two questions:

First, has there been a miscarriage of justice

Second, are there reasons not to speak about that miscarriage of justice

What are these reasons? From the victims perspective the argument boils down to an argument of the cause of death. Denying Ms Letby’s guilt does not imply justice goes unserved. There is not another murderer out there, unidentified, unpunished and living a high life, or continuing to offend. It means there was not a murder. It is hard to imagine the outlook of a grieving parents but it is hard to see why this would be a bad outcome.

If we assume campaigners are neither stupid nor acting in bad faith — the “fourteen experts“ are plainly neither — then it follows there is an argument to be had that this was a miscarriage of justice. It may not have been, but there is an argument. If this argument turns out to be right, then one implication is the babies were not murdered.

Serial killer trophies

It is alleged that Ms. Letby took handover sheets home with her and kept them as trophies of her grisly deeds:

The prosecution maintained that the applicant’s responsibility for the deaths and sudden collapses of the babies could be inferred from a raft of circumstantial evidence. [...] She retained and took home a large number of handover sheets as “trophies” of her crimes. These handover sheets were confidential documents and should not have been removed from the unit. Over 200 were found hidden under the applicant’s bed.

Now — look, I am not a serial murderer, so I really wouldn’t know, but ride with me a while — a shoebox full of your own scribbled notes seems an odd serial killer trophy. Doesn’t it?

Serial killers may take trophies, the internet tells us, as souvenirs or keepsakes from their victims or as a way of remembering to maintain a sense of control over their victims.

But in this way, as in so many respects, Ms. Letby just thumbs her nose at what is expected of her as a self-respecting psychopathic killer.

The literature says the most common trophies are underwear or hair. Ed “Leatherface” Gein made furniture and suits out of his victims. Some, such as Jack the Ripper, Charles Albright, Stanley Baker, Jeffrey Dahmer, Alex Mengel and Dennis Nilsen kept severed body parts. Others took jewellery, driver’s licences and personal effects. One took a library card. But all took things that, in some way or another, belonged to or personified the victim and signified her control and possession of things in the world. These were trophies of conquest: of deprivation of that control.

So what about your own scribbled handover sheets, which you made yourself, had in your bag anyway, and were never in the victim’s control? As trophies these seem — well, a bit beige, don’t they?

But, look: ok. Let’s go with these handover sheets as potential serial killer trophies. Clearly, they might, also, not be. It could be an accident: it could be sloppiness. (Nurses on the internet are ferociously divided: some say it would be unthinkable, ever, to take so much as an annotated lunch ticket off the ward. Others claim to pull sheaves of the things out of their smocks each day before putting the wash on.) It certainly seems precendented: it happened often enough at the very same Countess of Chester Hospital to make the papers independently.

So for now, let us give Ms. Letby the benefit of the doubt and allow that, in itself, it might denote behaviour that is merely sloppy, or even within the Overton window of normalcy.

Are there some other filters we might apply to this trove of sheets to bump up the inferential likelihood of evil?

There are.

One is the subject matter of the sheets. If they all relate to victims, and only victims, then, hello: that seems a bit more fishy. handover sheets about random shifts on which nothing much happened don’t seem especially emblematic of anything.

To be sure, some do relate to victims. We are not told whether they relate to specific shifts on which collapses occurred, but it seems reasonable to suppose that, if they did, the Crown would be all over that fact in its summing up. It was not. Of the handover sheets, Mr Johnson KC said:

I’m not going to spend a lot of your time looking at Lucy Letby’s notes. There are more important things in this case.

Later, on day 2 of his summing up, Mr Johnson KC said:

I want to start — I’m not going to deal in great detail with these jottings. I’ll start with Exhibit 15, which is the handover sheet of Baby P] and [Baby O].

Lucy Letby suggested that she took this home deliberately to rely on it as an aide-memoire when writing up the drugs on her following shift. But when you look at page 2, which shows the back of this document, the only drug you will see recorded on that sheet is caffeine. So Lucy Letby’s explanation is not true.

Why is she not prepared to tell you the true reason?

It can’t be because it helps her, can it? We suggest that the handover sheets are capable of informing you of her unhealthy interest in some of these children.

Whether directly, as in the case of [Baby M] for example, or indirectly, as in the case of [Baby G], for example, whose handover sheet would have been a very useful reminder of how to spell her mother’s French name when conducting a covert Facebook search.

And when determining or considering Lucy Letby’s credibility, her believability generally, we encourage you to think about these things. First, her claim that her collection of handover sheets, acquired over years and retained through multiple house moves, was simply a consequence of her tendency to collect paper.

Second, her assertion that they were stored confidentially, her inconsistent assertions about owning a shredder and whether or not students receive handover sheets. Third, her assertion that the word “keep” written on the side of the shredder box at her parents’ house referred to the shredder rather than the handover sheets that were in the box.

And fourthly, her assertion that documents containing sensitive information about dead babies were, to use her word, insignificant.

None of that stands up to any sensible analysis. And as I say, if she’s not telling the truth about that, is the true explanation one that’s going to help her in the context of the allegations being made in this case? You can safely conclude the answer to that question is no.

We can see, the Crown did not really lean into the “murder trophy” argument. Indeed, it did not even mention it. It presented Ms. Letby’s explanations for having the handover sheets as evidence of her disingenuity. Mr Johnson thought the sheets were all somehow hinky, but did not offer a theory for why Ms Letby kept them. The best he can do is venture that it would help her spell a French surname for a covert Facebook search.

He didn’t like the explanation that she was a “magpie” — but, well, we’re back to our old friend base rates: American Psychiatric Association’s DSM-5 classifies “hoarding disorder” — which this was nothing like — as affecting 2-6% of the population. That is quite a bit more likely an explanation than “serial murder trophy”.

As back-pedals go, “spellchecker” is quite climbdown from “serial killer trophy”. As a hypothesis seems extraordinarily weak. And the bigger picture suggests why: the 257 handover sheets found in her possession spanned not the 15 months of the charges, but her whole career, and just 21 of them — fewer than 1 per cent. — related to victims of the alleged crimes with which she was charged at all, let alone “critical shifts”.

There’s a killer on the ward...

Given that “insulin poisoning” is such a popular way for serial murderers to practice their craft, and since it is held in a tightly controlled environment, why has the system not been adjusted to better control for access to insulin? There are two possible answers: first, a sustained systemic failure of healthcare agencies to implement trivial steps to prevent murder; secondly: these “insulin cases” have other explanations and are not, in fact, the work of serial murderers. Comparison of the relative base rights (of other explanations for insulin readings and serial murders) might be interesting.

The trial went for ten months, so there was a full hearing of the issues

This is true, but — having done jury service twice — this is no guarantee that the jury will be any the wiser. In fact, synthesising information over even a week is a job, and much of the proceeding is opaque; there are stops and starts, and the cross-examination can be extremely oblique. The only way the jury — none having specialists legal or medical training — can get a handle on the material is to have a big picture narrative and hang the reams of detail on that frame — and where it doesn’t seem to fit, discard it: we are pattern-matching machines. Good cross-examination technique is never puts a big picture theory to the defendant much less allows her an open hand to respond to it with her own narrative — but rather is designed to chip away at a witness’s credibility with tight, closed, leading questions which probe miniscule lapses in recollection and inconsistencies, often deliberately shearing them from their context, where possible concealing from the witness their relevance to the overall prosecution theory — to avoid the defendant anticipating and disarming any prosecution “gotchas“. This seems mean, but in an adversarial system it makes sense: it is the defence barrister’s role to open up that wider context (but again there are strict rules about what you can say: you cannot ask your own witness leading questions. In any case, cross-examination will often seem like the barrister is giving evidence, but technically she is not: only the witness’s answers are evidence. This is often lost on court reporters, so we should not be surprised if it is not obvious to lay jurors. There is a re-enactment of sections of Ms. Letby’s cross examination on YouTube. It is slow, laborious fine-grained stuff. Much of it is meaningless unless you know what the barrister is driving at, and party is the art is to conceal that. Realistically, a jury gloms onto a couple of key facts, that is all she wrote. If the facts were (a) There definitely was a malicious actor on the ward in at least a couple of cases (the “insulin poisonings”) — Ms. Letby acquiesced to this, and it seems the Defence accepted it — and (b) that the only person with the opportunity to be that malicious actor for all cases was Ms. Letby which, again, the defence conceded, then ten months of tedious court procedure might not be enough to shift that narrative.

The Court of Appeal Judgment

You haven’t read the Court of Appeal judgment so you can’t possibly know. True, in denying leave to appeal, the Court of Appeal effectively heard the appeal and flatly rejected it, giving thoroughly reasoned grounds. However, a legal appeal is a constrained, formalistic process. The grounds on which one can appeal are narrow, limited largely to questions of law and not fact: the court will generally not override the findings of a jury unless the evidence was manifestly unable to support a conviction. This is an extremely high threshold, for reasons of public policy. A defendant cannot introduce new or better evidence that it could have called at the original trial. If the defence had evidence but for strategic reasons the defence chose not to call it, then it is tough: you don't get a second bit at the cherry.

The grounds for Ms. Letby’s appeal application were narrow points of law:

1. That the judge was wrong to reject the defence’s application to dismiss the charges at the end of the prosecution case on the grounds of “no case to answer“ — that the prosecution evidence, by itself, was so weak and its witnesses so unreliable that there was no possibility of a conviction:
2. That the judge was wrong to tell the jury that it could convict if it were sure that there were murders, even if it wasn't sure exactly how the murders were committed

Insulin inference

Regarding the “concrete” insulin evidence, the prosecution argued: “if the jury could agree that Ms. Letby had deliberately poisoned two babies, they could also reasonably conclude that she had harmed others using different methods even if the evidence in those cases was less concrete.”: (Sub point: some of those who criticised the trial were at the trial).

Improbable cluster

The jump in annual deaths from three to seven and eight strongly indicates foul play: not according to the, er, statistics.

Circumstantial evidence

Circumstantial evidence speaks for itself — oh, there’s that confusion about probabilities again.

Motivation of innocence campaigners

Two strands of this:

1. “Innocence campaigners use the families’ grief to build their own reputations”
2. Innocence campaigners only care because she seems like a nice, pretty white girl: leaving aside what a generally despicable insinuation this is, for many of us, it just isn't right: for many of us, Ms. Letby’s personal identity is neither here nor there — for all I know she may be guilty — but more that this fits a disturbing pattern where the justice system is systemically generating outcomes that seem, on hindsight and taking a wider perspective than the formal legal procedural one, extremely troubling. The Post Office Horizon scandal, Andy Malkinson, the Sally Clarke situation — it seems that the entire system is designed, from the ground up, to generate bad outcomes in certain cases: Expert witness incentives: the admissibility of inferential probabilities, crown policies on investigating statistics. Legal/judicial infacility with probabilistic reasoning. These factors contrive to produce or at least encourage bad outcomes. That is why there is concern. None of this has anything to do with pretty white girls. (Note: neither Andy Malkinson nor the sub-postmasters count as “pretty young white girls”)

Virtual red-hands

Dr. Jayaram caught Ms. Letby “virtually red-handed”, standing over desaturating babies, doing nothing.

Covered tracks

Ms. Letby “covered her tracks” by erasing data from hospital records, changing records. In particular, erasing records of Baby E’s mother’s visit and Ms. Letby’s own presence with the baby at the time of its collapse: there seems to be little direct evidence of this — it is inferred from incomplete hospital records or inconsistencies with witnesses who claimed to have been present (i.e., she must have altered them) — which is one explanation: another is that witnesses were mistaken or — given the allegation of under-resourcing and mismanagement, another (and most likely) is that the records were never made, or not kept. Most of the allegations of record tampering were put to Ms. Letby by the prosecution during cross examination, by way of challenge to her evidence in chief, and not by witnesses. These allegations are not evidence, as such. The one case where Ms. Letby agreed she changed a record, by one hour, her evidence was that she did it because the original annotation was incorrect. Again, no actual evidence was called to contradict this.

Circumstantial evidence again

It’s no big deal that the case is only about circumstantial evidence: Lots of people get convicted on circumstantial evidence alone. Differences between circumstantial cases where there definitely was a murder (e.g. David Bain) with circumstantial cases where there was not (Lindy Chamberlain). Witness the Thirlwall kerfuffle about extubation rates while Ms. Letby was at the Royal Liverpool. How would extubation data arise? Presumably, it does not auto-generate, but is collected by those observing extubations—e.g., rostered nurses? Even if mandatory there is an element of discretion here: a diligent nurse would generate “worse” stats than a slipshod one. So —. (This is the problem with circumstantial evidence, in a nutshell: it does not “speak for itself” (pace Ken Macdonald KC) but requires an imaginative, narrative act of inference. The same data permits many, contradictory inferences. The difference is not the evidence, but your inference. Circumstantial evidence is not “facts”.) Lucy Letby: the judge’s direction

Prosecution hypothesis becomes evidence

Often, the prosecution will put its own theory of the case - its own inference — to a witness who, not having grounds to doubt it, adopts it, converting it from a theory to evidence. For example, in cross-examination, the crown asserted — inferred — that because babies were recording unusually high insulin levels, their glucose bags must have been tampered with by someone. Ms. Letby — allowing for the moment that she knew no better than anyone else whether it was true — acquiesced to the suggestion, presumably because it seemed plausible and she could not think of another explanation. But there was no evidence it was true and subsequently other theories have arisen that could have explained it that did not require tampering. Likewise, some timing and door swipe evidence that suggested a baby was left to desaturate for thirty minutes was put to a doctor who explicitly said, “Well I don't recall anything, but if that’s what the data says, I suppose that must be true.” It turned out much later the door swipe data was wrong. In the most egregious cases the prosecution put their theory to a witness — was they are obliged to do — who rejected the assertion, but it was still replayed in the media as “evidence which emerged at trial”. For example, the assertions that Ms. Letby altered time records to mask malicious interventions. She denied all these allegations but one, and that one she explained she changed to correct an earlier error. The crown offered no evidence to directly contradict this — to be sure, none may have been available, and that does not mean it was not true — and while it is of course for the jury to assess a witness’s credibility, disbelieving a witness’s denial is different from presenting positive evidence supporting the assertion: a disbelieved denial of the allegation, “You doctored the glucose bags, didn’t you?” is not evidence that the defendant did doctor the glucose bags. It is an inference that she did. Much of the weight of the putative “evidence” against Ms. Letby was of this kind: not evidence at all, but inference. But inference needs to come from evidence. All we have by way of direct asserted evidence is that of the expert witness and the consultants.

Bad faith

There’s no need to suggest anyone acted in bad faith. This is the essence of prosecutor’s tunnel vision: a series of cognitive biases lead into a logical cul-de-sac it is hard to get out of. The same biases can also apply to innocence campaigners. but the “guilty” campaign will find it harder to back out of their cul-de-sac. The innocence case commits only to the weak proposition that “there is reasonable doubt”. It is easy enough to walk that back. It is harder to resile from the proposition: “I have no doubt”.

Because of the co-dependency of the circumstantial evidence, the case depends on an all-or-none approach. The argument cannot stand case that Letby was responsible for some collapses, but not others, because evidence for the individual cases would not by itself discharge the burden of proof. That Ms. Letby was somehow causative of collapses is a long way short of saying she wilfully inflicted them. She may have been causative by omission. By choosing the wrong option in an emergency situation. Perhaps her clinical practice was ineffective. Perhaps she was negligent — even reckless, in individual cases. The prosecution case obliges us, in those cases, to attribute to malice what is more probably caused by error.

Interlude

Probabilities are confusing things.

Say a nurse works, on average, 56 hours per week. she will be on duty for one-third of the week, or one shift in three. A year comprises 1095 eight-hour shifts. We would expect our nurse to work 365 shifts on average.

How safe is a guess that our nurse will work at least 25 shifts in the year? Yes, barring unexpected events, she almost certainly will. We can choose 25 shifts from the 365 she actually worked quite easily: We have 317,289,491,593,508,738,514,256,079,646,867,087,834 different combinations of twenty-five shifts! Still, that number is minuscule compared to all possible permutations of 25 shifts from the whole 1,095.

Which twenty-five? Well, there are a lot of choices. 365 is a much bigger number than 25, so we can see immediately the odds are very close to one.

The amateur expert serial murderer

The unit’s lead consultant Dr Stephen Brearey first raised concerns about Letby in October 2015.

No action was taken and she went on to attack five more babies, killing two.

— BBC website

On the face of it, the intensive care unit in a neonatal hospital — which must be as tightly controlled, monitored and overwatched as any place in Britain — is the last place you would embark on a regime of surreptitious serial murder. Better, surely to do it like Harold Shipman did, in the privacy of your consulting rooms, or better still, during a house call.

And once the hospital’s lead consultant had his own suspicions about the Nurse, you would think, she would be under even greater surveillance. Wouldn’t she? So does this not make the lack of direct evidence even more remarkable?

Caption text

Category	Daniela Poggiali	Lucia de Berk	Jane Bolding	Lucy Letby
“Incriminating” evidence	Took selfies laughing with dead body She had the ability to switch between wings of hospital Fiery temper, played pranks on colleagues Found patients irritating Allegations of thefts of jewellery	Example	Example	Googled parents That post-it note The increased insulin without corresponding C-peptide in 2 victims Had lots of teddy bears
Motive	“She must have just loved killing people”	Example	Example	Example
Actual evidence	Correlation between shifts and deaths	Example	Example	Correlation between shifts and deaths
Mitigants	Large ward many patients High proportion of very old and terminally ill patients Data collection was pretty ropey	Example	Example	Example
Alleged Method	Pottassium Choloride	Example	Example	Several
Resources	Richard Gill blog	Example	Example	New Yorker article We need to talk about lucy letby podcast

More Witches

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Peasant 2: Burn her!
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Woman: And this isn't my nose it's a false one
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Peasant 2: Yes.
Peasant 3: Yes.
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Peasant 2: Burn her anyway!
Peasant 1: Burn her!
Bedevere: Quiet! There are ways of telling whether she is a witch.
Peasant 1: Are there? What are they? Tell us.
Bedevere: Tell me, what do you do with witches?
Peasant 1: Burn them!
Bedevere: What do you burn apart from witches?
Peasant 1: More witches!
Peasant 2: Wood.
Bedevere: So, why do witches burn?
Peasant 1: Because they're made of wood?
Bedevere: Good!
Bedevere: So, how do we tell whether she is made of wood?
Peasant 1: Build a bridge out of her!
Bedevere: Can you not also make bridges of stone?
Peasant 1: Oh, yeah.

David Holmes

JHB: what could have been the tell-tale signs that this woman was a danger? Was there anything that could have given us forewarning? Holmes: “Well, it may not give forewarning but generally speaking, [with] a serial killer of this stature really it’s almost obligatory to have psychopathic traits and they will often show themselves in various ways. ... she was very controlled. She was trying to give the image of a very responsible, caring nurse who would be there in a crisis to save babies and so on and so forth. So she is playing the role of someone who would not be suspected other than the correlation between her and the babies’ deaths.”

“It’s a situation where you have not got any really concrete evidence: one piece, like a CCTV camera footage or a witness, etc, all you’ve got is an accumulation of basically very low-level evidence — coincidences, etc — but when you actually accumulate a large number of these [using] something called a Bayesian analysis, it’s actually more statistically sound to have 100 little arrows pointing towards Lucy and none pointing away from her, and I think that’s how justice was actually reached.”

—Criminologist David Holmes on Sky News, 18 August 2023

Well, to a point. Bayesian analysis starts with a “prior probability” — an initial estimate of the likelihood that “Lucy Letby murdered multiple neonatal infants with no motive, no psychiatric history and no prior tendency” — which is extremely low — and adjusts it to a “posterior probability” on the cumulative effect of the “little arrows” to revise the likelihood of it being true. An accumulation of even weak “little arrows” can increase the “posterior” probability of the hypothesis, but if all the arrows are also consistent with another explanation, their contribution to updating a Bayesian analysis may be modest. There is significant potential for false positives when dealing with rare events and weak evidence. (Compare this with David Bain’s case, where the prior probability that he was the culprit was already high (the event was certainly murder, and he was one of only two plausible suspects), and the circumstantial evidence against him was strong, and Lindy Chamberlain, where the prior probability was very low, and the circumstantial evidence weak).

Prior and posterior probabilities in different cases

Case	There was a Murder		Suspect responsible		Another person responsible
	Prior	Posterior	Prior	Posterior	Prior	Posterior
OJ Simpson	Certain	Unchanged	Very likely	Greatly increased	Fairly unlikely	Unchanged
David Bain	Certain	Unchanged	Fairly likely	Greatly increased	Fairly likely	Greatly decreased
Peter Ellis	Very unlikely	Mildly increased	Extremely unlikely	Mildly increased	Extremely unlikely	Unchanged
Lindy Chamberlain	Very unlikely	Mildly increased	Extremely unlikely	Mildly increased	Extremely unlikely	Unchanged
Lucy Letby	Very unlikely	Mildly increased	Extremely unlikely	Mildly increased	Extremely unlikely	Unchanged

The question, then, is how many of the “little arrows” are inconsistent with another explanation. Here there are two categories of alternative explanation: that someone else was responsible, or that no-one was criminally responsible: the event would have happened anyway.

The prior probability of there being a different murderer on the ward is the same for any other nurse as for Lucy Letby: extremely unlikely. No suggestion was made that any other person was involved, so we can assume two alternatives: either an innocent explanation or Letby was the culprit.

It is worth also looking at the categories of circumstantial evidence in each case and associating it with one or other of those probabilities. Does it make it more likely that There was criminality involved in the deaths, or that, Assuming there was criminality, Letby was the culprit.

Relevance of evidence to probabilities

Evidence	Criminality		Letby was the culprit
	Relevance	Posterior value	Relevance	Posterior value
Ward roster	No	N/A	Yes	Contested
Post-it Note	No	N/A	Yes	Weak
Editing nursing notes to “cover tracks”	Yes	Weak	Yes	Contested
Post-event internet activity	No	N/A	Yes	Weak
“Trophy” handover notes	No	N/A	Yes	Weak
Bubbly personality	No	N/A	No	N/A
Obsession with a married doctor	No	N/A	No	N/A
Unexpected collapse	Yes	Weak	No	N/A
Insulin levels	Yes	Weak	No	N/A
Skin discolouration	Yes	Weak	No	N/A
Liver damage	Yes	Weak	No	N/A
Evidence of air in blood and brain	Yes	Weak	No	N/A

Interestingly, bar for the alleged editing of nursing notes, which case been oddly under-reported, none of the “small arrows” point to both the presence of criminality and Letby’s particular involvement. It is worth reviewing the published pieces of the chief “public prosecutors” who make the case for Letby’s guilt. Among these are the expert witness Dr Dewi Morris, Daily Mail Journalist Liz Hull, BBC Journalist Judith Moritz and the frequently interviewed Criminologist David Holmes. They are emphatic in their dismissal of the “yellow butterfly gang” — in Hull’s words, “diverse band of fanatics and pseudo-scientists” (later upgraded to a “strange band of misfits and ghouls”) coming from all “walks of society: well-to-do pensioners, middle-aged women, and the unemployed” and who, er, “counted scientists, neo-natal nurses, doctors and statisticians among their members” — so I was curious to see what they brought out as their clinchers.

Lizz Hull

Hull, on the New Yorker piece:

I’ve read the article and now the retrial is over I can write about it. And while there’s no doubting the author, who says she obtained full transcripts of the ten-month trial at huge cost, has researched the case thoroughly, it contains errors and cherry-picks evidence, omitting large parts of the prosecution case which was pivotal in reaching a conviction.

For example, it makes no mention of the 250 confidential “trophy” handover notes, blood test results and resuscitation notes relating to the babies police found at Letby’s home; it does not try to explain the Facebook searches that she made for the parents of her victims, years after she harmed their children.

Letby’s abnormal, animated behaviour in front of grieving parents after a baby died and pictures of cards she sent or received from parents of babies she murdered that were stored on her mobile phone, are also ignored, as is her obsession with a married doctor and her deliberate editing of nursing notes to make it seem like a baby was on the verge of collapse to cover her tracks.

In a later article on 24 July 2024 — the first one evidently not having the desired effect — Hull sets out the overlooked evidence that proves the conspiracy theorists (although they are better described as “no conspiracy theorists”) wrong.

Sewage and insulin

• No evidence was presented to show any of the infants contracted bacterial or parasitic infections linked to dirty water caused by drainage problems.
• Though journalists have since queried the suitability of the insulin tests for use in a criminal prosecution, the defence team did not.

Concession that the insulin was deliberate

The Court reporting suggests this was less emphatic than it has been made out to be:

Letby is asked if Child E was poisoned with insulin.
“Yes I agree that he had insulin.”
“Do you believe that somebody gave it to him unlawfully?”
“Yes.”
“Do you believe that someone targeted him?”
“No.”
“It was a random act?”
“Yes...I don't know where the insulin came from.”
“Do you agree [Child L] was poisoned with insulin?”
“From the blood results, yes.”
“Do you agree that someone targeted him specifically?”
“No...I don't know how the insulin got there.”
Letby adds: “I don’t believe that any member of staff on the unit would make a mistake in giving insulin.”

Liver injury

One of the babies suffered significant liver trauma. The post-mortem said the bleed was due to vigorous CPR, but a forensic pathologist from told the jury he’d only ever seen this type of extensive internal injury in children involved in road, trampolines cycling accidents, or who had been deliberately assaulted.

Letby accepted in evidence that the injury took place “on her watch”.

Air in stomachs

The Guardian reported that seven anonymous neonatologists called Dr Evans’ theory about the injection of air into the stomach via nasal feeding tubes “ridiculous”.

Dr Evans admitted to me that injecting air in a nasogastric tube is “utterly bizarre” and something he’d never heard of before. But he added: “That doesn't mean it can’t exist.”

The shift rota

The infamous shift rota chart was not created after the fact, so the “Texas sharpshooter” argument falls over. Dr Evans reviewed all cases bar one were looked at “blind” months, before Letby’s name was disclosed to him.

Dr Evans says Cheshire police did not put together the shift graph until he had identified suspected cases. Only when officers cross-checked those events with staff on duty did the striking pattern of Letby’s presence emerge.

The rash

The argument that prosecution expert witnesses misdiagnosed a rash based on misreading Dr Shoo Lee’s 1989 report on the air embolism phenomenon. Dr Lee told Letby’s appeal he believed the rashes were not diagnostic of the condition.

But Dr Lee did not have access to the medical notes or witness statements when making this assessment and his evidence was ruled inadmissible.

The screaming

Hull describes “harrowing testimony of parents, doctors and nurses” of uncharacteristic “screaming” from several of the premature babies, who likely suffered extreme pain.

Letby, the Prosecution said, had rammed a medical instrument down the boy's throat moments earlier, causing internal bleeding. She later injected him with air to kill him.

Letby’s behaviour

On one occasion Letby told a colleague a baby “looked pale” when no lights were on in the nursery, and her face was obscured by a canopy. That child had stopped breathing but was resuscitated only to die by alleged air injection the next day.

The cards, googling and condolences.

Bayesian probabilities applied to other questions

As Tom Chivers notes in his excellent Everything Is Predictable: How Bayes’ Remarkable Theorem Explains the World, a fellow newly armed with Bayesian techniques is the proverbial “man with a hammer”: once you learn how to do it, it is hard to resist applying it to all kinds of questions not usually seen as the domain of statistics.

For example: miscarriages of justice are, as far as we know, extremely rare: those in the population of murder convicts across history — which surely numbers in the millions — who were justly convicted enormously outweigh those who were unjustly convicted, which we can put in the hundreds or thousands (Wikipedia lists just fifty-four). This might lead to the conclusion that a person who has been convicted by a jury is, ipso facto, highly unlikely to be innocent: that is, after all, the fundamental design goal of the justice system.

But the number convicted of “medical carer serial murders” in history is also small. According to Wikipedia, of nearly 800 serial killers fewer than 60 were medical carers, of whom two-thirds admitted their crimes. Serial murder is rare. Medical carer serial murder is even rarer.

But amongst Healthcare serial murder cases, miscarriages of justice are comparatively common. There are at least five recent examples, all strikingly similar:

• Lucia de Berk: A Dutch nurse wrongly convicted of multiple murders due to statistical errors and misinterpretation of medical evidence. Her conviction was later overturned.
• Susan Nelles: A Canadian nurse accused of murdering infants; charges were dropped due to lack of evidence.
• Ben Geen: A British nurse whose conviction for murdering patients by inducing respiratory arrests was quashed on appeal due to unreliable evidence.
• Colin Norris: A British nurse convicted of murdering patients by insulin injection; his conviction was later overturned due to flawed medical evidence.
• Daniela Poggiali: An Italian nurse accused of murdering patients in a hospital. She was initially convicted but later acquitted on appeal due to a lack of conclusive evidence.
• Jane Bolding: A British nurse accused of murdering patients in her care. She was acquitted after a retrial due to lack of evidence.

The relatively high proportion of miscarriages of justice among “hospital carer” cases raises the “posterior probability” that a given conviction of this type might be wrongful by comparison with other types of murder case where such errors are historically less common.

The multiple modus operandi

An unusual feature, compared with even other hospital carer serial killer cases is the variety of ways by which Letby is alleged to have murdered, or attempted to murder, the children.

• Insulin in intravenous bags
• Injection of air into bloodstream
• Injection of air into stomach via gastric tube
• Dislodging feeding tube
• Liver trauma
• Overfeeding by milk

Two points of significance here: first, serial killers generally develop and stick with a single modus operandi, refining a technique that “works” and avoids leaving evidence or allowing for detection. Leaving no evidence is hard. Second, the more different routes one uses, the more scope there is for evidence or detection.