Lucy Letby: the judge’s direction

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That judge’s direction

Mr Justice Goss instructed the jury:

“You don’t need to be know how she did it as long as you are sure she did it”.

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

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 within a time window in which the defendant was the only person to be in contact with the victim, and there is eyewitness evidence of a heated argument after which the defendant announced he was going to murder the victim. Immediately afterward, the defendant is arrested in possession of a hammer, a club and a lead pipe, all of which are covered in the victim’s blood. There no doubt that the defendant was responsible for the murder: there is evidence that the defendant used each weapon, but it is not clear with which she administered the deadly blow.

The jury is not obliged to acquit the defendant because they do not know which weapon she used, if they are sure she used a weapon. The inference that the defendant murdered the victim does not depend on the evidence of a specific weapon. The burden of proof is already satisfied: the identity of the weapon is an extraneous detail.

Ms Letby’s case, the equivalent scenario would be that, independent of evidence of a method of murder, there existed independent evidence that Ms Letby was unequivocally responsible: that all reasonably plausible means of death involved Ms. Letby’s malice.

This would mean first ruling out as a reasonable explanation death by natural causes, medical misadventure short of recklessness by Ms Letby, or medical misadventure of any kind by anyone else.

Only then can the jury be sure that Ms. Letby was responsible, regardless of what she actually did.

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

There are different scenarios:

1. Death definitely has 1 of 3 causes, the defendant definitely was responsible for all 3, jury need not be sure which of the 3 it was. Does not apply here: no direct evidence, no finite set of causes. Some natural causes.
2. Death definitely has 1 of 3 causes, defendant definitely responsible for 2. Jury must be sure it was not the 3rd cause. Between the other 2, 1. above applies. Does not apply here for same reason as 1.
3. Death definitely has 1 of 3 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.