A half-dozen pediatric doctors and toxicology experts said on Thursday that jurors were misled by prosecutors who cited unreliable and misrepresented insulin tests during the trial of Lucy Letby, a nurse convicted of murdering seven babies at a British hospital.
The doctors made their assertions in a new report that Ms. Letby’s lawyer submitted to Britain’s Criminal Cases Review Commission, which is responsible for investigating possible miscarriages of justice, in the hopes of being allowed to pursue a full appeal of her 15 life sentences.
Ms. Letby, who worked as a nurse in a neonatal unit at a hospital in northern England, was found guilty in 2023 of deliberately harming — and in seven cases, murdering — babies by injecting them with air, overfeeding them with milk, infusing air into their gastrointestinal tracts or poisoning them with insulin.
In the new report, the six experts, who include a forensic toxicologist, a professor of forensic science and an endocrinologist who has written multiple peer-reviewed papers on medical test errors, attacked the validity of the evidence of insulin poisoning used by the prosecution at trial.
“Our inescapable conclusion is that this evidence significantly undermines the validity of the assertions made about the insulin and C-peptide testing presented in Court,” they wrote in a summary of the report provided to reporters by her legal team.
Ms. Letby has always maintained her innocence. Since her two trials, serious questions have been raised about her guilt, including in a 13,000-word New Yorker article last May. But efforts by her lawyers to reopen the case with a full appeal have been repeatedly denied.
The new report focuses on two babies — known as babies F and L — whose blood sugar levels dropped to low levels, but who later recovered. Ms. Letby was convicted of trying to murder the two babies by adding insulin to their food, causing a condition called hypoglycemia.
Tests suggested that the babies had high levels of insulin but only a negligible amount of C-peptide, a substance detected when insulin is produced by the body. The prosecution argued the insulin must therefore have been administered externally.
In the new report, the experts present what they describe as “convincing new evidence from multiple sources” showing serious problems with the test results used to demonstrate that Ms. Letby poisoned two of the babies with insulin.
They said the test, called “the Roche immunoassay,” was known to result in “falsely high insulin results.” They also argued that there were other ways for infants to receive insulin, including through the placenta while they are in their mother’s womb.
The experts said that when evidence was presented to jurors about the levels of insulin found in the small infants, the prosecution referred to the wrong data.
“Studies in adults and older children were quoted which are not relevant, and the limited appropriate information was not referred to,” they wrote.
They said the testing “did not meet acceptable forensic standards” and that the results of the Roche test, in particular, should not have been relied on without being confirmed by more precise laboratory tests.
The Royal Liverpool Hospital laboratory where the tests were conducted explicitly warns in its online guidance that they are “not suitable” for investigating low blood sugar created by an insulin injection. “If exogenous insulin administration is suspected as the cause of hypoglycemia, please inform the laboratory so that the sample can be referred externally for analysis,” it says. But both babies recovered, so their samples were never referred anywhere else.
The experts said that prosecutors and the police had not considered other ways that the babies became hypoglycemic besides foul play.
“There are alternative medical explanations which explain the hypoglycemia in both babies, such as line failure, sepsis and perinatal stress-induced hyperinsulinism,” they wrote. “These alternative possibilities were not considered.”
Questions about the accusations of insulin poisoning have been raised publicly by doctors in the months since the trial. Thursday’s 86-page report is an effort by Mark McDonald, Ms. Letby’s lawyer, to present those questions to the commission in a formal way.
“The conclusions of the report on Babies F and L clearly demonstrate that the case must go back to the Court of Appeal as a matter of urgency,” Mr. McDonald said in a statement.
He added: “Lucy Letby is currently serving 15 whole life terms in prison, when overwhelming independent expert evidence indicates that no babies were murdered.”
In a statement to a public inquiry last month, lawyers representing some of the families of babies who died or were harmed at the Countess of Chester Hospital said: “The families have no doubts about Letby’s guilt.”
Mr. McDonald also submitted to the Criminal Cases Review Commission a full 698-page examination of Ms. Letby’s case by a separate panel of experts, led by the renowned Canadian neonatologist Dr. Shoo Lee, who previewed their findings in February. That report concluded that “there was no medical evidence to support malfeasance causing death or injury in any of the 17 cases in the trial.”
