This is not just about one terrible set of allegations. Health, the law, checks and balances: it is testing public confidence in everything

Beyond reasonable doubt. Those words carry a heavy moral burden, and so they should. Jurors hold another human being’s life in their hands, and must be convinced there is no other rational explanation for the facts presented to them than the defendant’s guilt. But what happens when those facts start to shimmer and blur, to multiply and divide confusingly before your eyes?

Lucy Letby is officially Britain’s worst serial child killer, serving 15 life sentences for murdering seven babies and trying to kill seven more. But her case has become as troubling to some medical professionals as it is attractive to conspiracy theorists because of the stubbornly persistent doubts at its heart. There are things we may never know for sure about those babies’ last moments.

Gaby Hinsliff is a Guardian columnist