Lucy Letby: the judge’s direction

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In his summing up to the jury, Mr Justice Goss instructed the jury:

“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; in some instances there may have been more than one. To find the defendant guilty, however, you must be sure that she deliberately did some harmful act to the baby the subject of the count on the indictment and the act or acts were accompanied by the intent and, in the case of murder, was causative of death [...].”

As a principle of law, this is undoubtedly correct, and serves to resolve a probabilistic paradox which might otherwise arise.

Say a defendant is charged with murder. There is unimpeachable evidence that the victim died as a result of violent blunt trauma to the head during a period in which only the defendant had contact with the victim and that took the shape of a heated argument culminating a threat to beat the victim senseless. Immediately afterward, the defendant was caught in possession of a hammer, a club and a lead pipe, all covered in the victim’s viscera. There was no doubt that the defendant murdered the victim but it was not clear with which implement.

The law is rightly clear this does not matter. The defendant’s guilt does not depend on which of the implements she used to administer the fatal blow. The burden of proof is satisfied: the precise weapon is an extraneous detail.

But this is an unusual case. All other potential causes of death can be ruled out. The victim’s manner of dying excludes an innocent explanation: blunt trauma is not consistent with an episode of hypoglycemia, so if the victim’s head is caved in, we need not waste time investigating the chance of a contemporaneous hypoglycemic episode.

Alternatively, independent direct evidence might positively suggest the defendant’s intervention. An unusually high insulin reading might be consistent with undiagnosed hypoglycemia, but if the defendant was witnessed administering insulin to the victim ten minutes before she collapsed, it becomes a far less probable explanation.

In Ms Letby’s case, the equivalent scenario would be that all reasonably plausible means of death involved Ms. Letby’s malice. Given the evidence, no explanation not involving the defendant’s malice is l reasonably plausible.

But here the victims’ “manner of collapse” does not imply malice. In every collapse that led to a formal medical examination, the original conclusion — based on the best evidence — was natural causes.

And nor did any independent evidence positively suggest Ms. Letby’s intervention in the collapse. There is no evidence that Ms Letby obtained any insulin, let alone administered it, nor that she injected air, overfed or assaulted any of the victims.

We are not in a situation where “all plausible causes of death involved Ms Letby. There are plausible innocent explanations.

So the second part of the judge’s direction, not the first, is the important part.

You must be sure that she deliberately did some harmful act.

It is hard to see how a jury could be sure Ms Letby did some harmful act without compelling evidence as to what that act was.

Unless, of course, the persuasive implicating evidence was the implausible coincidence. Once my be happenstance, twice coincidence, but by the time we get to the fifteenth occasion we are surely past the point of even enemy action. But this is not positive, active evidence, but deduction. Its credibility can only be assessed by a probabilistic analysis, and one was not carried out.

Now these findings are not determinative of Ms. Letby’s innocence, but they do indicate there are plausible alternative explanations such that the jury cannot be sure, without better evidence, that Ms Letby was responsible.

The judge later directed the jury:

“In the case of each child, without necessarily having to determine the precise cause or causes of their death, and for which no natural or known cause was said to be apparent at the time, you must be sure that the act of acts of the defendant, whatever they were, caused the child’s death, in that it was more than a minimal cause. The defendant says that she did nothing inappropriate, let alone harmful to any child. Her case is that the sudden collapses and deaths were or may have been from natural causes or from some unascertained reason or from some failure to provide appropriate care and were not attributable to any deliberate harmful act by her.”

There are different scenarios:

1. There are a finite number of potential causes, the defendant was responsible for all of them, jury need not be sure which was the operating cause. Does not apply here: no direct evidence, no finite set of causes. Some natural causes.
2. There are a finite number of potential causes, defendant definitely responsible for a defined subset of them. Jury must be sure it was a cause from that subset. Between the remainder, 1. above applies. Does not apply here for same reason as 1.
3. There are a finite number of potential causes, defendant may have been responsible for all of them. If they do not know which it was, Jury must still be certain defendant was responsible for all three. Does not apply here: Same as 1 above. In Ms. Letby’s case, there were an unknown set of possible causes, some innocent, some malign, it was not clear she was even responsible for the malign ones. Since you can’t rule out unknown innocent causes, if they don’t know how Ms. Letby committed the acts, the jury can’t be “sure” she committed them.