EXCLUSIVEThe truth about all the disputed Lucy Letby evidence: As claims she is innocent grow louder, read the definitive breakdown by GUY ADAMS

Two different juries and four of the most senior judges in the land concluded that Lucy Letby was one of the most prolific serial killers of modern times. 

Yet ever since she was convicted of murdering seven newborn babies and attempting to murder six more, a growing army of sceptics including medical experts has decided the verdict against her is deeply flawed. 

Yesterday, in part one of his analysis of the case, GUY ADAMS looked at the crucial areas of evidence, from the confessional notes she wrote to suspicious alterations to medical records. Here, he continues his forensic examination...

Lucy Letby was found guilty of murdering seven babies and attempting to kill six more while working as a nurse during 2015 and 2016

Disputed evidence

Case for guilt

Much of Letbys testimony was disputed by colleagues. Some was provably false.

In an apparent effort to gain the jurys sympathy, she complained for example about being arrested while wearing pyjamas. In fact, she was frog-marched out of her home in a blue tracksuit.

Prosecutor Nick Johnston KC asked Letby if she wanted the court to see a video of the incident, but she did not respond. You tell lies deliberately, dont you? he added.

During police interviews, Letby claimed to be unaware that an air embolism (of the sort that affected four of the babies she was convicted of harming) could affect children, saying shed not been trained about the condition.

In fact, shed completed a training course immediately prior to the period when the killings began in which she replied air embolism to a question about the potential risks of delivering medication via a long intravenous line. And in a text message to a colleague in 2016, shed warned of the risk of an air embolism when carrying out a different procedure on an infant.

Letby told police she had not been taught about air embolism in infants, but there was strong evidence to indicate otherwise

Then came an occasion when nurse Ashleigh Hudson told how Letby had entered a nursery in the middle of the night and warned her that a baby, Child I, looked pale.

At the time, no lights were on, the childs face was obscured by a canopy, and Letby was standing by the door several yards away, making it highly unlikely that she could observe this unless she already knew the symptom was there.

Under cross examination, Letby, who was accused of force-feeding milk and air to the child, said she was able to notice the babys skin colour because she was experienced, so I knew what I was looking for. Realising that this might suggest she was previously aware the child was seriously unwell, she then appeared to correct herself, changing for to at.

Case for innocence 

Letby gave evidence over 14 days, with nine of them devoted to her being quizzed by the prosecution.

Some supporters argue that some factual inconsistencies are to be expected, given the immense pressure she found herself under and the amount of time that separated the events under discussion and the eventual trial. Whats more, they say, no apparent motive for the alleged crimes ever emerged during trial.

Others point out that she was not the only one who made errors. During Letbys re-trial, on charges of attempting to murder an infant referred to as Baby K, it emerged that door-swipe data showing when doctors were entering and leaving the intensive care ward, had been mis-labelled during the original court case. Rather than showing when someone was leaving, it indicated when they were coming into the room.

The neo-natal unit of the Countess of Chester Hospital, where Letbys crimes took place

This was a significant blunder. The prosecution had previously argued that Letby was alone when Dr Ravi Jayaram, a consultant, claimed to have walked in and seen her standing over the infant, whose breathing tube had been dislodged.

In fact, the updated data revealed that the childs assigned nurse had entered three minutes earlier, though that didnt stop the jury in the retrial convicting her of attempted murder.

Letby also attempted to appeal against her original conviction by claiming that the judge failed to properly investigate a complaint phoned into the court during the final days of the trial by a member of public who claimed to have overheard a juror saying theyd made up their minds from the start about her guilt.

In fact, the complaint was extensively probed, the Court of Appeal ruled, finding it had been made maliciously by the owner of a cafe who was in dispute with the jurors partner over the sale of an iPhone.

A row over insulin

Case for guilt

Letby was found guilty of attempting to murder two babies by injecting synthetic insulin into their feed bags. This aspect of the case against her hinged on tests that suggested extremely high levels of the substance were present in their blood when they collapsed.

In court, Letby agreed with prosecutors that someone had unlawfully given insulin to the two babies by tampering with the bags. However she denied being that person: Insulin has been added by somebody. How or who I cant comment on, only that it wasnt me. I dont believe that any member of staff on the unit would make a mistake and give insulin.

An expert witness, Professor Peter Hindmarsh, testified that blood test results indicated that one of the children, Baby F, had been given a contaminated feeding bag over a period of 17 hours. The other, Baby L, had been poisoned over two days. He calculated that the latter would have required two or three bags of feed. The jury concluded that Letby was responsible.

Case for innocence

Initially there was no suspicion of foul play, and because both babies survived, the tests were not checked at a proper forensic lab. Instead, they took place at a clinical lab of the Royal Liverpool University Hospital.

According to an NHS guidance note, such testing cannot usually be used to infer whether insulin has been administered artificially. They merely indicate what level it is at in a patients blood. Whats more, the samples were not checked by forensic experts and could not be re-tested, as would usually happen in a court case, since they were disposed of in the normal way. Some say this renders the evidence unsafe.

A police search takes place at Letbys home during her arrest

Professor Alan Wayne Jones, an expert in forensic chemistry, believes this renders these two convictions unreliable, saying the tests are not proof of foul play in a criminal prosecution for murder.

He previously raised similar concerns over Colin Norris, a Leeds nurse convicted in 2008 of murdering four patients using insulin. He remains behind bars, but in 2021 the Criminal Cases Review Commission referred his case back to the Court of Appeal.

There are also questions about timing of these alleged attacks. Letby was not recorded as being present at the Countess of Chester during a period when at least one of the feed bags seems to have been administered. For her to have been behind this poisoning, she must therefore have left a contaminated bag in a fridge, hoping a colleague would use it. Does this seem credible? Critics think now.

The suspicious rash

Case for guilt

In seven cases, Letby was convicted of harming babies by injecting air into their bloodstream, causing what is known as an air embolism. These were principally identified via a strange rash which had appeared on their bodies around the time of collapse, often shortly after Letby had been seen in the company of the infants.

Although air embolism is a relatively rare condition, the prosecution cited a 1989 paper by a Canadian neonatologist named Shoo Lee as evidence that this was the likely cause of death.

Expert witnesses who reviewed X-rays of several victims were also used to identify what appeared to be bubbles of gas in their bodies. Owen Arthurs, an eminent Cambridge-educated radiologist based at Londons Great Ormond Street Hospital, found unusual columns of air in the major blood vessels of Babies A, D, and O.

The jury was also shown a striking X-ray of a line of gas in a blood vessel along Baby Ds spine which, in the absence of a fracture or infection, Professor Arthurs said, must have been injected into her circulation.

A pathologist named Dr Andreas Marnerides, who also gave evidence, found a bubble of air in Baby As brain and lung at post-mortem, and said Baby D had gas in a blood vessel in her belly.

Case for innocence

Supporters of Letby do not think this cause of death was ever established beyond reasonable doubt. In particular, several experts have criticised doctors use of rashes to identify embolisms, the most notable of whom is the aforementioned Dr Lee.

The academic, who is one of Canadas most eminent specialists, believes none of the cases of skin discolouration described in accounts he has read of the Letby trial sound like the type that, in his experience, indicate that an embolism has occurred.

Giving evidence to the Court of Appeal, Lee said that the only sign of the condition that could be relied on involves a rash featuring pink blood vessels superimposed on a pink or blue background. He did not believe witnesses who gave evidence in court had described such a rash (though conceded that hed not actually seen medical records of the affected children, or accessed the full witness statements).

The appeal judges ruled Dr Lees evidence was inadmissible, pointing out the defence could have called him to testify at the original trial, but chose not to. Other doctors who have spoken out in recent weeks say skin discolouration is an unreliable means to diagnose an embolism, since rashes can have a huge number of causes, particularly in infants.

Expert witnesses 

Case for guilt

The police investigation and eventual prosecution of Lucy Letby was assisted by no fewer than seven expert witnesses, who variously offered evidence that helped build the case against her.

But for a cruel twist of fate, there would have been an eighth, too. Dr Martin Ward Platt, who was instrumental in setting up the first neonatal network in northern England, was hired to assess the work of Dr Dewi Evans, the expert who first concluded that children were dying from air embolisms. He too agreed that Babies G, I, O and Q all likely had air injected into their naso-gastric tubes (The jury failed to reach a verdict in Baby Qs case).

Dr Dewi Evans, the expert who first concluded that children were dying from air embolisms

Dr Ward Platts report, which the Mail has seen, arguably goes further than those shared in court because he identifies another baby boy, whose case was not part of either trial, who was likely hurt this way. However it was never presented to the jury because the doctor developed a terminal illness and died in 2019 before the trial began.

Case for innocence

The defence barrister, Ben Myers KC, did not call his own expert witness. But he certainly instructed one, in the shape of Michael Hall, a retired neonatologist who was expected to point out flaws in the prosecutions theory that babies had been killed or harmed by air embolism.

Hall attended much of the trial. Critics regard the failure to call him as a significant tactical error that may render the conviction unsafe.

There is, for what its worth, a second possibility: that Myers, a hugely competent barrister, decided that Halls evidence might prove counterproductive were he to be cross-examined in court.

To that end, it seems significant that his written report into the death of Child A, which has been seen by the Mail, concludes that his cause of death was unascertained but does not rule out air embolism or that a member of staff deliberately injected air to cause harm.

If air embolism was the cause of Baby As death it could have come about as a result of either inadvertent or deliberate actions taken by staff caring for him, it states.

Other deaths

Case for guilt

Perhaps the most important piece of evidence against Letby involved a serious liver injury and internal bleeding suffered by Baby O – the first of two triplet brothers murdered on consecutive shifts, in June 2016.

An original post-mortem said the bleed was caused by vigorous CPR. But expert witness Dr Marnerides, a forensic pathologist from Guys and St Thomas Hospital in London, told the jury hed only ever seen this type of extensive internal injury and haemorrhaging in children involved in road accidents, or whod fallen from trampolines or bicycles, or whod been deliberately assaulted.

Letby was Baby Os designated nurse. She accepted when she gave evidence that the injury took place on her watch.

Evidence that Letby was involved in more deaths and injuries is meanwhile mounting. Expert witness Dr Evans has reviewed 82 potential new cases for the police, while the Public Inquiry was on Thursday last week told that detectives are investigating the time she spent on placement at Liverpool Womens hospital in 2012 and 2015.

Richard Barker KC, representing the families of victims, said several babies had collapsed there due to breathing tubes being dislodged. Such events typically occur in less than one percent of shifts, he said. But an audit has discovered that tubes were dislodged on 40 percent of the occasions when Letby was on duty.

Case for innocence

Letbys defence revolved around the suggestion that she was being scapegoated by colleagues and NHS managers for the deaths of babies caused by serious failures at the Countess of Chester.

To this end, they called Lorenzo Mansutti, the estates manager at the Countess of Chester Hospital, to give evidence. He told the jury that plumbers were called out five times to drainage problems at the unit in 2015 and 2016, leading to claims that sewage back-ups could be behind some deaths. However, no evidence was presented at trial to show any of the infants contracted bacterial or parasitic infections linked to dirty water.