Two Experts Leave Lucy Letby's Defence Team Over Science Dispute

Helen Shannon and Geoff Chase have withdrawn from Lucy Letby's defence team. The pair left the team on Monday, Sept. 14, 2026, over concerns about scientific credibility, according to reporting published that day The Guardian. Shannon is a British expert in chemical engineering. Chase is a professor of bioengineering based in New Zealand.

Shannon and Chase said some arguments advanced on Letby's behalf were inconsistent with the available evidence, science and established physiology, the way the body normally functions. Their objection was not to re-examining the convictions. It was to the terms on which parts of that re-examination were being made.

The broader context here is why that difference matters. It divides support for a review from support for how some claims in that review were argued.

Shannon and Chase are not supporters of the prosecution case. In 2025 they produced a 100-page report casting doubt on Letby's convictions for poisoning two babies with insulin. They said then there was a very strong level of reasonable doubt about those two convictions. They say they stand by that assessment. In their account, it was very unlikely anyone poisoned the two infants in the insulin cases. Their departure therefore separates continued scepticism about the insulin findings from unwillingness to endorse other claims now circulating in Letby's defence.

Convictions under challenge

Letby is a former neonatal nurse serving 15 whole-life orders after convictions across two trials at Manchester Crown Court The Guardian. A whole-life order means imprisonment for life without release. She was convicted of murdering seven babies and attempting to murder seven others between June 2015 and June 2016. The offences occurred at the Countess of Chester hospital in north-west England.

The insulin cases form a discrete part of that larger set. In 2023 Letby was convicted of attempting to murder two infants, known as Baby 6 and Baby 12, by spiking their feeding bags with insulin. The prosecution case turned on laboratory results, clinical course and interpretation of insulin and C-peptide physiology. C-peptide is a marker the body releases when it makes its own insulin, so it helps distinguish natural insulin from injected insulin. Shannon and Chase focused their 2025 report on that physiology and on alternative explanations for the test results.

Other convictions rest on different mechanisms. Letby was accused of injecting air into the blood of Baby O as well as other babies BBC. The prosecution said injected air caused an air bubble. The defence challenge has therefore had to address several distinct clinical theories, not a single method.

Trial evidence included testimony from Dr Dewi Evans, who acted as an expert witness for the prosecution The Guardian. Evans became a central and contested figure after the verdicts. A key prosecution witness in the murder trial was later reported to be under investigation by his employers BMJ.

Letby has failed in two attempts to challenge her convictions at the Court of Appeal in London The Guardian, the court that reviews serious criminal convictions. The appellate route is now largely closed. Attention has shifted to the Criminal Cases Review Commission, the statutory body that can refer convictions to the Court of Appeal where new evidence or argument creates a real possibility the convictions would not be upheld.

Mark McDonald began representing Letby in August 2024 and leads her defence team. In February 2025, lawyers for Letby launched a new bid to overturn her conviction for killing seven babies Reuters. That bid was supported by an expert panel which concluded the babies died due to natural causes or errors in medical care, with no evidence of deliberate harm The Guardian.

The Commission has been reviewing Letby's convictions for 18 months after receiving a dossier of evidence submitted in 2025. That review is the live procedural forum. It is separate from public debate and from press conferences by supporters or critics.

What the split changes

The broader context here is that the defence effort has grown more public, more international and more scientifically diffuse. It now brings together lawyers, neonatologists, statisticians, engineers and campaigners. Such coalitions can generate momentum. They can also generate friction over standards of proof.

In my view, the Shannon-Chase withdrawal sharpens that friction in a way practitioners will recognise. The CCRC tests new material for cogency, reliability and capacity to alter the safety of a conviction. Material that divides its own proponents on questions of physiology is harder to present as coherent fresh evidence. The Commission will assess documents, not endorsements. But internal disagreement over method can affect how an advisory report is weighed.

Looking at what this means for the next phase, three questions stand out. First, whether McDonald's team narrows its CCRC submissions to grounds with broad expert agreement, particularly the insulin cases where Shannon and Chase maintain their doubt, or continues to advance a wider set of challenges to air embolism, interpretation of collapses and other clinical findings. Second, whether replacement experts can be instructed on terms acceptable to both the legal team and the scientific contributors. Third, whether the prosecution's original expert evidence will itself face formal re-evaluation, either through the CCRC or through regulatory scrutiny of individual witnesses.

None of those questions reopens the convictions by itself. The whole-life orders stand. The Court of Appeal refusals stand. The path to referral runs through new evidence or legal argument capable of meeting the statutory test, a test designed to be exacting after jury verdicts in long trials.

The broader lesson here for readers who follow miscarriage-of-justice cases is procedural rather than polemical. High-profile reviews often expand as new volunteers join. Expansion brings competing theories. Courts and commissions then filter those theories aggressively. A defence that disciplines its own scientific claims early tends to preserve credibility with that filter. A defence that does not risks having stronger points discounted alongside weaker ones.

Shannon and Chase have not retracted their criticism of the insulin convictions. They have withdrawn their association from arguments they consider unsustainable.

In my view, how McDonald responds, and how the CCRC treats the dossier already before it, will determine whether this becomes a brief internal rupture or a lasting division over how to contest one of the most consequential criminal convictions in recent English legal history.