In the long and troubled aftermath of Lucy Letby's 2023 conviction for the murders of seven infants at the Countess of Chester hospital, the scientific scaffolding of her appeal has begun to show visible fractures. Two of her most prominent expert witnesses — chemical engineer Helen Shannon and bioengineering professor Geoff Chase — withdrew from her defence team on Monday, declaring that certain arguments being advanced on her behalf contradict established science and physiology, even as they maintain serious doubts about two of the insulin poisoning convictions at the heart of her case. Thei
Key experts withdraw from Letby defence over scientific credibility concerns
Seven babies were murdered and seven others were subjected to attempted murder by Lucy Letby at Countess of Chester hospital between June 2015 and June 2016.
Some arguments are inconsistent with science and established physiology
Mark
So two of their own experts just walked away. What does that actually tell us about whether Letby's convictions are sound?
Mimi
It tells us the experts still believe there's serious doubt about the insulin poisoning cases. That hasn't changed. But they're saying some of the other arguments the defence team is making don't hold up scientifically, and they won't attach their names to them.
Luke
Right, but we need to be careful here. Shannon and Chase are saying some arguments are "inconsistent with available evidence." We don't know exactly which arguments, or how fundamental the disagreement is. The barrister is saying they have other experts who support the broader case.
Mimi
That's fair. The letter is vague about specifics. But the fact that they're invoking professional ethics codes and saying they'd face sanctions if they stayed—that suggests real substance to their concerns, not just a minor quibble.
Mark
Does this help or hurt Letby's chances with the CCRC?
Luke
Honestly, it's ambiguous. On one hand, it shows the defence case isn't monolithic—there are limits to what even sympathetic experts will endorse. On the other hand, McDonald is right that a case doesn't live or die on one expert. The CCRC has been reviewing this for 18 months. They're presumably looking at the full dossier, not just Shannon and Chase.
Mimi
And there's the inquiry report coming Tuesday. That's going to document all the ways the hospital failed to act on warnings. That's a separate question from whether Letby actually did what she was convicted of, but it changes the context.
Mark
So we're waiting on the CCRC, and we don't really know what they'll do.
Luke
Exactly. The experts' withdrawal is a real event, but it's not a verdict on the convictions themselves. It's a statement about professional boundaries.
Der Puls
- Two of Letby's most credentialled scientific supporters have publicly broken with her defence team, warning that some of its arguments are not scientifically defensible and could expose them to professional sanction in two countries.
- The fracture is not a full repudiation — Shannon and Chase still assert 'very strong reasonable doubt' about the two insulin poisoning convictions — but their refusal to endorse the broader defence strategy has handed critics a significant moment of leverage.
- Letby's barrister has pushed back, insisting the case rests on a convergence of independent international experts in insulin, endocrinology, and laboratory medicine whose findings collectively undermine the trial evidence — no single expert's exit, he argues, changes that.
- The Criminal Cases Review Commission, eighteen months into its review, now faces a defence landscape that is publicly contested from within, complicating its task of determining whether a miscarriage of justice has occurred.
- Tuesday's publication of the Thirlwall Inquiry's findings on hospital leadership failures will layer institutional accountability over an already volatile scientific and legal dispute, ensuring that the families of the seven murdered babies and seven survivors remain at the centre of an unresolved national reckoning.
In the long and troubled aftermath of Lucy Letby's 2023 conviction for the murders of seven infants at the Countess of Chester hospital, the scientific scaffolding of her appeal has begun to show visible fractures. Two of her most prominent expert witnesses — chemical engineer Helen Shannon and bioengineering professor Geoff Chase — withdrew from her defence team on Monday, declaring that certain arguments being advanced on her behalf contradict established science and physiology, even as they maintain serious doubts about two of the insulin poisoning convictions at the heart of her case. Their departure arrives on the eve of a public inquiry's findings into the institutional failures that allowed harm to continue unchecked, reminding us that in cases of this gravity, the pursuit of truth is rarely a single, unified endeavour.
Two of the most prominent scientists supporting Lucy Letby's bid to overturn her convictions stepped away from her defence team on Monday, citing concerns they could no longer reconcile with professional integrity. Helen Shannon, a chemical engineering specialist, and Geoff Chase, a bioengineering professor based in New Zealand, informed the Criminal Cases Review Commission that certain arguments being advanced by Letby's legal team were 'inconsistent with the available evidence, science and established physiology' — and that endorsing them would place both experts at risk of sanction under engineering codes in their respective countries.
The withdrawal is not a wholesale abandonment of doubt. Shannon and Chase had previously produced a substantial report arguing there was 'very strong reasonable doubt' about two of the insulin poisoning convictions — those involving babies known as Baby 6 and Baby 12 — and they have not retracted that position. What they could no longer support was the full scope of the defence strategy, which they warned was placing Letby's long-term interests, and the interests of the affected families, at serious and unnecessary risk.
Letby, a 36-year-old former neonatal nurse, was convicted in 2023 of murdering seven babies and attempting to murder seven others at the Countess of Chester hospital between June 2015 and June 2016. She is serving 15 whole-life sentences. Her barrister, Mark McDonald, responded to the experts' departure by stressing that the case rests not on any single voice but on a convergence of independent international specialists in insulin, endocrinology, and laboratory medicine — each, he argued, identifying fundamental problems with the scientific basis on which the jury convicted.
The timing of the withdrawal is freighted with significance. On Tuesday, Lady Justice Kathryn Thirlwall's public inquiry is expected to publish its findings on how hospital leadership failed to act on doctors' repeated alarms about unexplained deaths on the neonatal unit in 2015 and 2016. A separate criminal investigation into potential corporate manslaughter at the hospital is also underway. As institutional failures are about to be formally documented, the scientific case against Letby's conviction is simultaneously fracturing in public view — leaving the CCRC to weigh competing expert testimony and determine whether the case warrants a return to the Court of Appeal.
Two of the most prominent scientific experts supporting Lucy Letby's bid to overturn her convictions have stepped away from her defence team, citing irreconcilable concerns about the credibility of arguments being advanced on her behalf. Helen Shannon, a chemical engineering specialist, and Geoff Chase, a bioengineering professor based in New Zealand, withdrew on Monday after months of collaboration with Letby's legal team. Their departure marks a significant fracture in what has been presented as a coordinated expert challenge to the evidence that secured her conviction.
Letby, a 36-year-old former neonatal nurse, was convicted in 2023 of murdering seven babies and attempting to murder seven others at the Countess of Chester hospital in north-west England between June 2015 and June 2016. She is serving 15 whole-life sentences. The two insulin poisoning convictions—involving babies known as Baby 6 and Baby 12—have been central to her case, and Shannon and Chase produced a 100-page report last year arguing there was "very strong reasonable doubt" about whether those two infants were actually poisoned at all.
Yet in their letter to the Criminal Cases Review Commission, the watchdog body examining whether her convictions represent a miscarriage of justice, Shannon and Chase made clear they could no longer stand behind the full scope of arguments their defence team was mounting. Some of those arguments, they wrote, were "inconsistent with the available evidence, science and established physiology." They stated plainly that they could not support them "as scientifically credible" and that doing so would expose them to professional sanction under engineering codes in both the UK and New Zealand. The experts said the defence strategy was placing Letby's long-term interests "at serious, unnecessary and unacceptable risk" and that the consequences extended to the families of the babies who died and were harmed.
The withdrawal comes as a public inquiry led by Lady Justice Kathryn Thirlwall prepares to publish its findings on Tuesday. That review is expected to document a series of missed opportunities for hospital leadership to intervene after doctors raised alarms about unexplained deaths on the neonatal unit in 2015 and 2016. A separate criminal investigation is underway into potential corporate manslaughter and gross negligence manslaughter at the hospital itself. The timing creates a complex landscape: as institutional failures at the hospital are about to be formally documented, the scientific foundation of Letby's conviction is being contested—but now with visible cracks in the expert consensus she has been relying upon.
Mark McDonald, Letby's barrister, responded by emphasizing that the case does not depend on any single expert or argument. He said the defence now has evidence from multiple leading international experts in insulin, endocrinology, and laboratory medicine that "fundamentally undermines" the scientific evidence presented at trial. He argued that the strength of the new evidence lies in its "breadth and convergence," with independent experts from different disciplines and jurisdictions identifying fundamental problems with the scientific basis the jury used to conclude the babies were deliberately poisoned.
The CCRC has been reviewing Letby's convictions for 18 months and declined to comment on the experts' withdrawal. The commission's decision will ultimately determine whether the case proceeds to appeal. What remains unresolved is whether the departure of Shannon and Chase signals genuine scientific weakness in parts of the defence case, or whether it reflects a disagreement over strategy and risk tolerance among experts who fundamentally doubt the poisoning convictions but differ on how far to push alternative explanations. The distinction matters enormously: one reading suggests the defence case is fragmenting under scrutiny; the other suggests a disciplined retreat from overreach by experts protecting their professional standing.
Bemerkenswerte Zitate
Some of the other arguments now being put forward we cannot support as scientifically credible and which have, in our view, fundamental unresolvable problems.— Helen Shannon and Geoff Chase, in letter to CCRC
We now have evidence from a number of leading international experts in insulin, endocrinology and laboratory medicine which fundamentally undermines the scientific evidence relied upon at trial.— Mark McDonald, Letby's barrister
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