Lucy Letby is serving 15 whole-life orders after a jury found she murdered seven babies and attempted to murder seven others at the Countess of Chester Hospital between June 2015 and June 2016. Those convictions have not been quashed. Two applications for leave to appeal failed. What has changed is the status of a piece of science that sat near the centre of the prosecution case, and the idenтιтy of the man now attacking it. Dr Shoo Lee, a Canadian neonatologist, professor emeritus at the University of Toronto and founder of the Canadian Neonatal Foundation, co-wrote a 1989 paper on pulmonary vascular air embolism in newborns. Prosecutors used that paper to support the claim that some babies collapsed after air was injected into their circulation. Lee later said the paper had been misread. Skin discoloration, which the Crown treated as a telling sign, was not in his view diagnostic of air in the bloodstream. He has since published further work arguing that the patchy marks described in the Chester cases do not match what his research actually showed. In early 2025 he went further.

He convened an international panel of senior clinicians, working unpaid, and asked them to review the medical records without deciding guilt or innocence. Reporting of the panel’s membership has described neonatologists, a paediatric surgeon, an infectious-disease specialist and a neonatal nurse drawn from Canada, the United States, Japan, Germany, Sweden and the United Kingdom, among them Neena Modi, a former president of the Royal College of Paediatrics and Child Health. At a London press conference Lee summarised their conclusion in the bluntest terms available to him: they had not found murders. In the cases they reviewed, he said, death or injury was explained by natural disease or by substandard care.

Mark McDonald, Letby’s barrister, called the material compelling and said it demolished the air-embolism theory. The panel’s own summary report was careful on one point that campaigners often skip. It was instructed not to determine innocence or guilt, and it agreed that findings would be released even if they did not help the defendant. That does not make the report neutral in effect. A finding of no medical evidence of deliberate harm, if accepted, would leave the prosecution theory without its main mechanism. Critics of the panel note that it was ᴀssembled after contact with the defence, that it did not hear the trial, and that other clinicians who gave evidence for the Crown, including Dewi Evans and Sandie Bohin, stood by the view that air embolism was the best explanation in several cases.

A retired surgeon quoted in the British press has argued a narrower physical point: if babies had died of air in the heart, post-mortem examination should have found that air, and in his view the absence of such findings makes the mechanism impossible. Lee’s answer has been that the original paper was about a different pathway and a different pattern of signs, and that common neonatal events such as sepsis and circulatory collapse can discolour skin without anyone injecting anything. The Court of Appeal has already refused to treat his evidence on discoloration as a ground for reopening the case, on the basis that the prosecution had not relied on skin marks alone. The new battleground is therefore not the appeal that failed, but the file now sitting with the Criminal Cases Review Commission, which can send a case back only if it sees a real possibility that the conviction would not be upheld. Until that happens, Lee’s sentence and the jury’s verdict occupy the same public square: one says the science was misapplied, the other still says she did it.