Two experts who left Lucy Letby’s defence team over concerns about its “scientific credibility” have claimed that her barrister is harming her prospects of securing freedom.
Helen Shannon, a British chemical engineering specialist, and Professor Geoff Chase, a New Zealand-based bioengineering academic, were among an international group of doctors and scientists who last year supported claims that Letby may have suffered a miscarriage of justice.
The group compiled a 100-page report questioning Letby’s convictions for the attempted murder of two babies who were poisoned with insulin.
However, the pair said on Monday that they had withdrawn their support for Letby’s defence team, citing concerns over the “scientific credibility” of parts of its evidence and what they described as “unresolvable problems”.
They also accused Mark McDonald, the barrister leading Letby’s campaign to overturn her convictions, of “placing the long-term interests of Ms Letby at serious, unnecessary and unacceptable risk”.
Their intervention comes as the public inquiry into the murders is due to publish its findings today.
The inquiry, chaired by Lady Justice Thirlwall, is expected to identify several missed chances for hospital leaders to act after doctors warned of a sharp rise in deaths on the neonatal unit during 2015 and 2016.
Letby, 36, has consistently maintained her innocence. She is challenging convictions for murdering seven babies and attempting to murder seven others at the Countess of Chester Hospital between June 2015 and June 2016, offences for which she is serving 15 whole-life sentences.
The Criminal Cases Review Commission, the body responsible for investigating possible miscarriages of justice, is examining a dossier submitted on her behalf last year by the expert panel led by Canadian neonatologist Dr Shoo Lee.
At a press conference in February 2025, Dr Lee said that no murders had taken place, claiming instead that the babies died either from natural causes or as a result of poor care.
Ms Shannon and Professor Chase told The Guardian, although they stood by their assessment that it was ‘very unlikely’ the babies, known as Babies F and L in the trial, were poisoned, they could not support other evidence being used by Letby’s defence team relating to the insulin cases.
Letby was found guilty of murdering seven infants and trying to kill seven more
Her barrister Mark McDonald has been reported to the Bar Standards Board
Dr Shoo Lee wrote to an unknown number of doctors to ask them to review the medical notes of 17 babies involved in Letby’s trial
Other arguments being put forward were ‘inconsistent with the available evidence, science and established physiology’, they said.
In a letter to the CCRC, the experts said: ‘Whilst it is entirely legitimate for the defence to advance multiple arguments, some of the other arguments now being put forward we cannot support as scientifically credible and which have, in our view, fundamental unresolvable problems.’
Ms Shannon and Professor Chase said the strategy of Mr McDonald was ‘placing the long-term interests of Ms Letby at serious, unnecessary and unacceptable risk’ and that those ‘consequences also extend to the families’ of the babies who died and were injured.
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‘We cannot, with integrity, support arguments which are inconsistent with the available evidence, science and established physiology,’ they added.
‘After disclosing these concerns, continued association with arguments we believe are demonstrably inaccurate creates a serious ethical issue under the professional engineering codes governing us in New Zealand and the UK, and exposes us to professional sanction.’
Dr Lee claimed his experts had been assembled without bias to carry out an ‘objective review’ of the medical notes of the 17 babies that Letby was initially accused of murdering or trying to kill at her trial.
But in September their independence was called into question after it emerged he had written to the medics, saying: ‘We might be her (Letby’s) last hope.’
One senior neonatologist told the Mail he declined to take part in the panel for several reasons, including because of the leading nature of the language in Dr Lee’s email.
Then, in April, it emerged Mr McDonald had been reported to the Bar Standards Board for alleged professional misconduct.
Families of the killer nurse’s victims are understood to have made a formal complaint about him to the legal regulator.
The complaint is believed to centre on a letter written by Mr McDonald’s then-instructing solicitors that was leaked to the Sunday Times.
The correspondence, addressed to Cheshire coroner Jacqueline Devonish, requested that Letby be afforded ‘interested party’ status in upcoming inquests into the deaths of her victims.
But Richard Baker KC, representing the families, said his clients had been ‘extremely distressed’ to learn their babies’ names – which are protected by strict anonymity orders – had been in the letter and ‘recklessly disclosed to a third party’.
In response to the withdrawal of Ms Shannon and Professor Chase, Mr McDonald said the case for Letby’s innocence did not ‘stand or fall on any one expert’.
‘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,’ he said.
‘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 upon which the jury were invited to conclude that babies [F] and [L] had been deliberately poisoned.’
The CCRC, which has been reviewing Letby’s convictions for 18 months, declined to comment.
A police investigation into potential corporate manslaughter and gross negligence manslaughter at the hospital remains ongoing.