Lucy Letby’s Appeal Battle Exposes Criminal Law’s Uneasy Reliance on Expert Witnesses
When Lucy Letby was convicted of murdering seven babies and attempting to murder seven others at the Countess of Chester Hospital, the case seemed closed. The trial, one of the longest and most harrowing in modern British criminal law, ended with a jury delivering verdicts that echoed across the country: a nurse had deliberately harmed the infants entrusted to her care.
But the story has not ended. Nearly a year later, Letby’s new barrister, Mark McDonald, has reopened the debate — not just about her guilt, but about how the justice system uses and interprets expert medical evidence. The battleground now is not a neonatal ward, but the credibility of prosecution experts and the reliability of the courts that leaned so heavily on their testimony.
The Expert at the Centre of Controversy
At the heart of this clash is Dr. Dewi Evans, a retired paediatrician who served as one of the prosecution’s leading experts during Letby’s trial. His testimony was pivotal. He told jurors that the pattern of collapses and deaths could not be explained by natural causes or poor hospital conditions alone. In his analysis, deliberate interference — air injections, insulin overdoses, blunt-force trauma — explained what happened.
But McDonald now argues that Dr. Evans has shifted his position. He claims Evans altered his conclusions on the deaths of three babies — referred to in court as Baby C, Baby I, and Baby P. In particular, McDonald says Evans once testified that Letby injected air through a nasal gastric tube, leading to their deaths, but has since revised his opinion.
If true, this is more than a medical detail. It goes to the core of whether the jury, and later the Court of Appeal, may have been misled about crucial evidence.
Evans Fires Back
Dr. Evans has not taken these claims lightly. In a sharply worded statement, he called McDonald’s accusations “unsubstantiated, unfounded, inaccurate.” He insisted the only adjustment to his evidence concerned the date of Baby C’s death, dismissing it as a clerical mistake rather than a scientific about-face.
In a BBC interview, Evans described McDonald’s approach as “most unedifying, most unprofessional,” and accused him of disrespecting the families of the victims. He acknowledged that expert witnesses can evolve their views as new evidence emerges — “that’s the scientific process,” he said — but denied that his conclusions about Letby’s culpability had shifted in any substantive way.
It’s an extraordinary public dispute. Rarely do we see an expert witness and a defence lawyer openly trading blows in the media. Yet that is what this case has become: a fight over credibility, disclosure, and what counts as “new evidence” in criminal law.
The Disclosure Question
McDonald’s central complaint is not just that Evans changed his mind, but that he wrote a new report on Baby C months ago — a report the defence has still not been given. If accurate, that could present a disclosure failure, one of the most sensitive issues in criminal law.
British courts have overturned convictions before on the grounds that prosecutors failed to hand over material that might have aided the defence. To McDonald, this is not about semantics. “The defence will argue that Dr. Evans is not a reliable expert, and all the convictions are not safe,” he said.
Evans counters that the only proper venue to test this is in court, under oath and cross-examination, not in press conferences or media leaks. He points out that the Court of Appeal has already endorsed his evidence and upheld the safety of Letby’s convictions.
A Case Built on Experts
The deeper issue is systemic. The Letby case is a vivid reminder that modern criminal law often lives and dies by the testimony of expert witnesses. In cases involving complex medicine — from sudden infant death to shaken baby syndrome — juries are asked to weigh technical evidence that even doctors sometimes disagree on.
This problem isn’t unique to criminal law. Personal injury claims, medical malpractice suits, and civil negligence trials also hinge on competing experts whose testimony can either make or break a case. Whether it’s proving a birth injury, a surgical mistake, or—as here—allegations of deliberate harm, courts rely on experts to bridge the gap between law and science. The danger is the same: when expert testimony is flawed, exaggerated, or misinterpreted, the outcomes can be devastating.
We’ve been here before. The wrongful convictions of Sally Clark and Angela Cannings, both mothers accused of murdering their babies, hinged on flawed or overstated expert testimony. In those cases, juries were swayed by what seemed like clear medical conclusions, only for those findings to unravel under scrutiny.
Letby’s critics argue that this parallel is being overstated — that her trial involved months of evidence, multiple experts, and careful deliberation. But her defenders see the same pattern repeating: a justice system too quick to anchor itself to expert testimony without sufficiently challenging its reliability.
The Appeal Hurdle
For Letby, the road to appeal is steep. She has already been denied permission twice. To succeed now, McDonald must convince either the Court of Appeal or the Criminal Cases Review Commission (CCRC) that genuinely new evidence has emerged.
That is where Evans’s alleged “revised” views come in. If they can be framed as a material change — not just a correction of dates but a fundamental shift — they may qualify as new evidence. If the courts see them as minor clarifications, the appeal could be blocked before it even begins.
Meanwhile, the Thirlwall Inquiry into the wider hospital failings continues, and Cheshire Police are still investigating other unexplained baby deaths. The legal machinery grinds on, but for the families, the uncertainty drags their grief back into public view again and again.
What This Case Tells Us About Criminal Law
There is no easy way to write about Lucy Letby. To the parents of the babies who died, suggestions of her innocence are unbearable. To her supporters, the idea that flawed expert evidence may have locked away an innocent woman is equally horrifying.
What is clear is this: the Letby saga is no longer only about one nurse and 15 convictions. It has become a referendum on how much weight we give to experts in criminal trials — and how well the system safeguards against their fallibility.
In criminal law, evidence must be beyond reasonable doubt. But when science itself is contested, doubt becomes a matter of interpretation. The battle over Lucy Letby’s convictions is now less about what happened in a neonatal ward in Chester between 2015 and 2016, and more about whether the legal system can admit the possibility that even experts, like everyone else, can be wrong.
