Shortly after Lucy Letby was sentenced to 15 whole-life terms for murdering seven infants and attempting to murder seven others between June 2015 and June 2016 – a conviction that made her Britain’s worst ever child serial killer – Cheshire police agreed to give “unparalleled and exclusive access” to the makers of a Netflix film about the case.

The finished documentary, The Investigation Of Lucy Letby, which is released on Wednesday, must be very different from what the producers envisaged when they first began work on the project, given the subsequent unexpected turns in the story. Since the two trials, the prosecution evidence and police handling of the case have faced criticism from an unprecedentedly large number of distinguished British and international medical experts. Led by the Canadian neonatologist, Dr Shoo Lee – who says again in the feature-length Netflix documentary that his research was misused to convict the nurse – many of the experts are convinced Letby is innocent, the victim of a catastrophic miscarriage of justice.

Their work is now ranged against the experts Cheshire police and later the Crown Prosecution Service relied on, led from an early stage by the retired paediatrician Dr Dewi Evans.

In the film, Evans recounts the now familiar story, that in May 2017 he read the Guardian’s report that Cheshire police had launched a criminal investigation into the deaths of babies at the Countess of Chester hospital in 2015 and 2016. Evans put himself forward for it, emailing a police contact, as he says with some relish: “Sounds like my kind of case”.

The film leaves out context necessary to understand how exceptional the theories Evans then produced were about how the babies died. There had been a coroner’s process: postmortems, an inquest and internal reviews at the hospital; an inspection by the Royal College of Paediatrics and Child Health; and reviews by external consultants. None found any evidence that any baby had suffered any deliberate harm. Evans looked at the same medical evidence and quickly decided differently.

There is no indication that the police officers went back to the original pathologists or sought more expert opinion at that stage about Evans’ novel diagnoses. Later they were supported by other prosecution experts. Det Supt Paul Hughes says in the film: “It was that sickening reality, that this could be murder of a baby. The next question we had to answer was: by who?”

Along with access, Cheshire police had promised the film-makers “never before seen” footage, but cannot have held anything that would have added anything material, as all evidence considered substantive would have been used at the trials. So, much of that footage turns out to be extended scenes of the three times that officers arrested Letby.

The use of this footage has already been criticised, including by Letby’s parents, for being intrusive and a breach of privacy. Letby is shown breaking down in tears the first time, at her own home; she was then arrested two further times at her parents’ house in Hereford, found in bed in her dressing gown the first time, and then ashen in a nightie at the next arrest, her teddy bear visible on the bedside ledge.

The evidence advanced against her is familiar now, but it is still instructive to see the police set it all out, including the shift chart, which matched Evans’ identification of 25 “suspicious incidents” to Letby, a hardworking young nurse who was often on shift.

Little context is given for the sinister interpretations of Letby keeping nurse handover shift charts, or her looking up some of the babies’ parents on Facebook. The film-makers pay more rounded attention to the notorious private notes Letby wrote, which included “I am evil, I did this” and “I killed them on purpose”. The CPS asked the jury to read this as a confession, but the notes were contradictory, anguished, with protestations of innocence. Letby also wrote: “I haven’t done anything wrong” and “I feel very alone and scared”.

Her lawyer, Mark McDonald, relates that – as first reported by Felicity Lawrence in the Guardian – Letby wrote the personal notes in mental distress after she had been removed from her job, and in counselling organised by the hospital, where she was advised to write her thoughts down. Letby has never confessed, and is shown in the police interviews consistently denying the accusations and saying that she loved her job.

Lee, shown first chopping logs at his expansive wheat farm in Alberta, flew in to London for the landmark press conference in February 2025, which he concluded with the line: “Ladies and gentlemen, we didn’t find any murders.”

His presentation included a recitation of his expert panel’s findings that all the babies died from medical causes and a catalogue of poor care. The mother of one baby is anonymously featured in the film, talking of her terrible ordeal and grief. Lee said the doctors had failed to give her antibiotics for hours after her waters broke, and the baby had died of pneumonia and sepsis – as the original postmortem found.

The mother agrees that the hospital failed her and her baby. But she adds, as a response to Lee’s analysis: “Every doctor, nurse, expert, all clearly said that [the baby] was improving. She was getting better, she was getting stronger.”

Hughes expresses no doubts over the convictions and is not shown engaging with the expert criticism. The most notable revelation comes not from the police, but from one of the Chester hospital consultants, Dr John Gibbs.

“I live with two guilts,” he says. “Guilt that we let the babies down, and tiny, tiny, tiny guilt: did we get the wrong person? You know, just in case: a miscarriage of justice. I don’t think there was a miscarriage of justice, but you worry that no one actually saw her do it.”

Tiny as he says it is, this appears to be the first public admission of doubt from one of the doctors over all that has happened since the babies died on their unit and they went to Cheshire police to accuse the nurse.