There are two parallel universes in the Lucy Letby story.
One can be witnessed every day in Liverpool at the public inquiry into her case. Here, the matter of Letby’s guilt is settled. The question for the judge is why Letby was able to harm babies for so long.
In the other universe, doubts about the evidence used to convict her have been mounting. Leading statisticians and medical experts are arguing Letby may be the victim of a miscarriage of justice.
It is a surreal state of affairs: a legal system that has decided Letby is a serial killer – and a debate outside that questions her guilt.
As journalists we have been covering the Lucy Letby case for years – through two trials, an appeals process, an ongoing public inquiry and the growing controversy over her conviction. We have written a book together and made two Panorama films about the case – the latest of which airs on Monday with new information, and hears from both leading critics and the prosecution experts now under fire.
Letby is officially the most prolific child killer of modern times – convicted of murdering seven babies and attempting to murder seven others. And yet her case divides opinion.
Had someone actually seen her harming a baby at the neonatal unit in the Countess of Chester Hospital, the case might have been more straightforward, but no-one did. There was no incriminating CCTV or DNA evidence either. The evidence against her was circumstantial.
The statistics
One of the documents that played a key role in her trial was a grid, listing the incidents in the case with ‘X’s to show which members of staff had been on duty. Letby was the only nurse on duty for all of them.
But the grid has attracted scorn from statisticians. They argue that we don’t know how the “suspicious events” listed on the grid were selected or which incidents were excluded, so on its own the grid is little more than a visual stunt. The jury also heard there were two suspicious incidents when Letby was not at work – neither of which was included on the grid.
But is the grid really the problem?
If there was undisputed medical evidence that 24 crimes had been committed, then surely the fact Lucy Letby was present each time would be damning.
And therein lies the key question of the Letby case: How convincing is the medical evidence that the baby deaths and collapses were definitely crimes rather than naturally occurring events?
The air embolism evidence
The most controversial evidence concerned allegations that Letby murdered babies by injecting air into their blood. That would cause an air embolism – a blockage caused by an air bubble in the blood circulation.
To do this, Letby would have to have taken a syringe and injected the air into the babies’ intravenous lines. These are normally used to administer fluids, drugs, and nutrition to ill or premature newborns.