A new Netflix documentary examines the criminal case of British nurse Lucy Letby and the contentious evidence that led to her convictions for the murder or attempted murder of 15 infants.
One of the major players from Letby’s legal saga is retired pediatrician Dr. Dewi Evans, who helped prosecutors build their case against her. The Investigation of Lucy Letby, which began streaming Wednesday, February 4, on Netflix, highlights Evans’s role as an expert witness in the shocking trial.
Here’s everything to know about Evans, his role in the investigation of Letby, and the methods he used to reach his conclusions—some of which are still debated today.
How Did Dewi Evans Get Involved With the Lucy Letby Case?
According to The Guardian, Evans, now 76, is a former consultant pediatrician with experience in neonatology, or specialized care of newborns. After his retirement in 2009, Evans began working as an expert witness.
In May 2017, Evans learned about the investigation of Countess of Chester hospital, where 17 infants had died and 15 more experienced “non-fatal collapses” over the prior two years. He immediately emailed a contact at the National Crime Agency, the British equivalent of the FBI.
“If the Chester police have no one in mind, I’d be interested to help,” he wrote. “Sounds like my kind of case.” Police followed up with Evans and, by July 2017, he began reviewing medical records for one of the babies in the case.
In July 2018, police announced they had arrested a female “health care professional” in connection with several infant deaths at Chester—later confirmed to be Letby. She was suspected of a role in the murder of eight infants and the attempted murder of six additional victims.
It would not be until her final arrest in November 2020 that Letby was formally charged, and she stood trial starting in 2022—setting up Evans’s crucial role in the case.
How Did Evans Say the Babies Died in His Initial Testimony?
Letby’s trial lasted 10 months and, because there was no forensic evidence and no one visibly witnessed Letby commit a crime, Evans’s testimony based on the victims’ medical records was crucial to the prosecution’s case against her.
Evans asserted the physical characteristics of the victims suggested that a caretaker—in this case Letby—had likely injected air into the babies’ bloodstreams, leading to their deaths. He referenced a 1989 research paper called “Pulmonary Vascular Air Embolism in the Newborn” and written by Dr. Shoo Lee and Dr. Alan Keith Tanswell. According to the final judgement of the case, Evans said that the infants whose records he had reviewed showed the skin characteristics of an air embolus.
The “descriptions of the clinical features of infants proven to have died from the effects of air embolus and described in many of the enclosed publications show marked similarities to the pattern of collapse and death of many of the babies,” he said.
According to the transcript, neither Evans nor Dr. Sandie Bohin, another lead expert for prosecutors, had any “significant, direct experience” of patients with an air embolus.
As we learned later, Lee had no knowledge of his paper being referenced in the case and was not asked to provide any of his own testimony. Letby was ultimately convicted of seven total counts of murder and eight of attempted murder at the trial and a subsequent retrial and is currently serving life in prison: one of only four British women in history to receive such a sentence.
Why Did Evans Changed His Conclusion for One of the Babies’ Deaths After Letby’s Trial?
Evans’s testimony in the case has become the subject of controversy.
During Letby’s trial, her lawyer, Benjamin Myers, accused Evans of making up alleged harms to support the case that Letby was guilty. He asked for Evans’s evidence to be disregarded, but the trial judge refused.
Around that time, a senior justice from a separate case accused Evans of breaching his duty of impartiality, saying he “makes no effort to provide a balanced opinion.” The retired pediatrician later boasted publicly he had lost only one court case over 35 years of experience as an expert witness. “That is entirely inappropriate. An expert should not be concerned about the outcome of a trial, only about providing independent evidence,” Gillian Tully, a professor at King’s College London, told The Guardian.
Evans refutes any claims of impropriety and says his track record speaks to his stringent research. “I would suggest that this indicates being careful. And thorough. It’s proof of my impartiality. Partisan witnesses don’t last long,” he said.
Still, he has seemingly shifted his stance on elements of Letby’s case. After her conviction, Evans filed an updated report about one of the victims, identified simply as “Baby C,” that contradicted the prosecution’s arguments. According to The Telegraph, prosecutor Nicholas Johnson told jurors that Baby C was killed by an injection of air into his stomach, citing an X-ray with a large bubble of air that Dr Evans deemed “suspicious.” It was later discovered that Letby was not on duty at the time of the X-ray and, thus, couldn’t have caused the air bubble.
Evans now insists that the dates were mixed up, and that the air was injected into the baby’s bloodstream at a later time when Letby was on duty. “I recognised the confusion at the trial,” he said.
However, Letby’s counsel, Mark McDonald, has claimed the new report shows the “evidence of their chief expert is now in doubt.” Reports have been submitted to the Criminal Cases Review Commission in an attempt to have her convictions overturned.
How Did Evans React to Recent Findings by Lee and a Medical panel “flawed”
Adding to the contention around Evans’s role in the case is the fact that Dr. Shoo Lee, the co-author of the paper cited in Letby’s trial, has since concluded details from the case show no signs of wrongdoing.
In February 2025, an international panel of 14 clinicians led by Lee determined there was no medical evidence to indicate Letby had injected air into the bloodstream of babies, or had committed murder. Another panel member said “there were highly plausible causes of death or deterioration,” and not signs of malfeasance.
Evans has since responded publicly to the panel’s findings, questioning their legitimacy and standing by his conclusions. “Forget the world leading experts. They were all recruited by this guy, Shoo Lee, who sent an email, which I’ve seen, saying, ‘You are the last hope,’” Evans told The Sun in February 2026. “In other words, they were in a corner before they took up the case."
“Shoo’s statements are the most flawed I have seen,” he added.
It’s not clear whether Evans directly participated in the new documentary, but it’s likely the film will explore his role in the case—and what the new findings might mean for Letby’s future.
Watch The Investigation of Lucy Letby on Netflix
According to the Netflix trailer, The Investigation of Lucy Letby features never-before-seen footage of Letby upon her arrest and new interviews with people connected to the case.
The documentary begins streaming on Wednesday, February 4.
Tyler Piccotti joined the Biography.com staff as an Associate News Editor and is now the News and Culture Editor. He previously worked as a reporter and copy editor for a daily newspaper recognized by the Associated Press Sports Editors. In his current role, he shares the true stories behind your favorite movies and TV shows and profiles rising musicians, actors, and athletes. When he's not working, you can find him at the nearest amusement park or movie theater and cheering on his favorite teams.
