All the questions raised about the Lucy Letby case as former minister set to launch probe

Tory MP David Davis is planning to raise a series of questions in parliament to further examine the evidence

Following 21 months of legal proceedings, Lucy Letby is now serving 15 whole-life sentences for seven murders and seven attempted murders of babies – and is widely considered the worst child serial killer in British history.

But despite the extensive legal hearings – comprising two trials and two unsuccessful appeals – some experts have sought to question her conviction, with Tory MP David Davis set to table a series of parliamentary questions in an attempt to further examine the evidence.

The former Brexit minister told The Independent: “I am intending to have a debate in September. It will give us time to go through the evidence – of which there is a vast quantity.

“With a lot of people claiming a mistrial including statisticians, nurses and senior medics, as well as reports of people being warned off giving evidence, it is clear we need to look at it quite closely.”

So which elements of the evidence against Letby – heard during the longest trial in British legal history – are some experts taking issue with?

While multiple juries, the family members of Letby’s victims, and many of her colleagues are convinced of her guilt, there were no direct witnesses to the murders of babies in her care between 2015 and 2016 at the Countess of Chester Hospital NHS Foundation Trust.

Instead, as is perfectly usual, the prosecution relied on circumstantial evidence such as presented testimonies from Letby’s colleagues, rota patterns and medical arguments. Here The Independent takes a look at the various areas some experts have raised questions over:

Lucy Letby was convicted of multiple murders and attempted murders (Cheshire Constabulary)

Statistical evidence

In September 2023, the Royal Statistical Society wrote to the chair of the newly announced public inquiry into the Letby case to warn generally that “it is far from straightforward to draw conclusions from suspicious clusters of deaths in a hospital setting”.

Expressing hope “that lessons from such cases in the past will be learnt”, the society’s leaders wrote: “It is a statistical challenge to distinguish event clusters that arise from criminal acts from those that arise coincidentally from other factors, even if the data in question was collected with rigour.”

One key piece of statistical evidence was the rota data which suggested Letby was always on shift when babies in the neonatal unit where she worked took an unexpected turn for the worse.

While one such chart listed 25 collapses and fatalities in which Letby was present, the jury was not told about a further six deaths over that period with which she was not charged, which were not included in the table, according to The Guardian.

The first review into the deaths was commissioned in July 2016, after fatalities at the unit rose from four each year in 2013-14 to an unusual spike of 13 deaths in the year to June 2016. That review found the unit was understaffed, with junior staff left feeling unable to call in consultants.

Letby when she was arrested and taken away by police (PA)

Deaths fell after Letby was removed from neonatal duty in June 2016, after colleagues raised concerns, while around the same time the unit was downgraded to stop taking the highest-risk premature babies.

John O’Quigley, a professor of statistical science at University College London, told the newspaper: “People get the wrong end of the stick with statistics. In my opinion there was nothing out of the ordinary statistically in the spike in deaths, and all the shift chart shows is that when Letby was on duty, Letby was on duty.”

A nurse ‘was told not to give evidence’

It was claimed on Sunday that a nurse who trained with Letby in Cheshire and wanted to support her was told by the hospital that she should not give evidence in her case.

The nurse said she was asked to be a character witness by the defence but her NHS trust advised her against getting involved, according to the Daily Telegraph. The nurse believed Letby was innocent and had been made a scapegoat for bad practice on the ward.

A second nurse, and a registrar who still work for the hospital, also told the paper they had been instructed by NHS bosses not to talk about the case, despite previously voicing their support for Letby.

The former nurse was given 15 whole life sentences (PA)

Air embolism

Analysis by the prosecution’s lead expert witness Dr Dewi Evans found that seven babies had been harmed by having air injected into them, which he said in some cases had caused fatal air embolisms, in others alongside other harms such as liver trauma or overfeeding.

While other expert witnesses agreed that babies could have had air injected into their stomachs feeding tubes inserted into their nose, or into their bloodstream, seven neonatalogy clinicians told The Guardian that they believed it implausible that injecting air into the stomach in this way could cause a fatal collapse.

Dr Evans also cited a 1989 academic paper on air embolism which described skin discolourations he and another expert believed were observed in several of the babies.

But the paper’s surviving co-author Dr Shoo Lee – who was not called upon by the defence in the trial – said in Letby’s appeal in April that he did not believe the descriptions of skin discolouration in the babies matched the type described in his paper.

No medical expert witness was called to challenge prosecution evidence

Neonatologist Dr Mike Hall was the specialist instructed for the defence, but was not called to give testimony before the jury.

He told The Guardian: “With regard to the medical evidence, I don’t think the prosecution proved she was guilty beyond reasonable doubt. I don’t think she had a fair trial because no medical expert witness was called for the defence to challenge the prosecution expert medical evidence.”

What other evidence was heard at trial?

Thousands of pieces of evidence were gathered for the first 10-month trial into Letby’s case, which led to her conviction in 2023 for the murder of seven babies and and attempted murder of six more – after around 110 hours of jury deliberations.

Among those were 257 confidential hospital documents such as handover and resuscitation sheets with medical details of her victims, including how many doses of adrenaline had been given to one baby during his collapse. Letby claimed she liked “collecting paper” or forgot to remove the documents from her uniform.

A search of her home also found a number of Post-it notes, on which she had written: “I killed them on purpose because I’m not good enough”, “I am a horrible person”, and “I AM EVIL I DID THIS”.

Letby herself spent 14 days in the witness box, facing close to 60 hours of questioning. The prosecution highlighted various instances in her testimony in which Letby appeared to contradict her own evidence to police, or disputed evidence she had previously agreed with.

Speaking to Sky News after her guilty verdicts, Dr Evans suggested the “smoking gun” had been when two of the babies were found to have very high levels of unprescribed insulin in their blood, which Letby herself conceded would mean they had been “deliberately” attacked, but again insisted: “Not by me.”