The public inquiry into the crimes of former nurse Lucy Letby opened in Liverpool last month, with its chair, Lady Justice Thirlwall, dismissing concerns about the safety of the convictions as 'noise'. However, questions continue to mount as Letby's new barrister, Mark McDonald, prepares an application to the Criminal Cases Review Commission, supported by expert medical evidence from leading neonatologists who believe there are more plausible alternative causes for the babies' deaths and collapses.
Criticism has centred on the use of a shift chart at Letby's first trial, which indicated which nurses were on duty when babies were allegedly attacked. Leading statisticians argue this represents a classic example of the 'prosecutor's fallacy', where an investigation begins with a suspicion and builds a case to support it, rather than rigorously exploring all possible explanations. Professor Jane Hutton of the University of Warwick described the evidence as 'a large pile of crockery, much of which is broken'.
The Thirlwall inquiry has heard that the police investigation was based on statistical coincidence from the outset. Hospital managers stated that when they approached Cheshire police in May 2017, they explained there was a 'notable high statistical relationship' between Letby and baby deteriorations, but no other evidence. Assistant Chief Constable Darren Martland noted it was 'uncomfortable' as there was no specific allegation of a criminal act. Five days later, Cheshire police opened a criminal investigation.
Emails seen by the Guardian reveal that in April 2018, a police officer contacted Professor Hutton to ask if she could quantify the likelihood of one staff member being on duty during all deaths and collapses. Hutton advised that a proper statistical inquiry should not focus on one individual from the outset but should examine all possible explanations, including medical conditions and unit performance. Despite this, Cheshire police signed a consultancy agreement with Hutton.
