Lucy Letby - Police and CPS handling of case adds to concern over convictions

When the public inquiry into the crimes of the former nurse Lucy Letby opened in Liverpool last month, its chair, Lady Justice Thirlwall, dismissed concerns about the safety of the convictions as “noise”. The judge cautioned that questions being raised were increasing the distress of parents whose children had died or been harmed.

- David Conn Felicity Lawrence

Letby was found guilty across two trials of murdering seven babies and attempting to murder seven others at the Countess of Chester hospital in 2015 and 2016. Thirlwall pointed out that in May this year, the court of appeal had refused Letby permission to appeal, and she said it was not the role of her inquiry to review the convictions.

Yet questions about the case, and the number of experts raising them, have continued to mount. Letby is being represented by a new barrister, Mark McDonald, and a number of specialists - including leading neonatologists - doctors who specialise in treating premature babies - are voluntarily working with him on an application to the Criminal Cases Review Commission.

Having examined the detail, these experts consider there are more plausible alternative causes of the babies' deaths and collapses than those for which Letby was convicted.

The Guardian can now report on further key concerns about the case, including the approach taken by Cheshire police and the Crown Prosecution Service, and the conduct of the trials.

“The prosecutor's fallacy”

At Letby's first trial, the prosecution used a chart that showed which nurses were on shift when babies were allegedly attacked. The chart was presented to the jury to illustrate the central allegation that Letby was the one constant presence. Its use has prompted unusually vocal criticism from leading statisticians. They argue that the chart represents a classic example of the “prosecutor's fallacy”, in which an investigation starts with only a suspicion, and a case is built to support it, rather than all possible evidence and explanations having been rigorously explored.

Jane Hutton, a professor of statistics at the University of Warwick, said of the shift chart and other elements of the case: “It's a large pile of crockery, much of which is broken. Such a pile does not hold water, however big it is.”