1. DYING BABIES

It all starts when a small group of doctors at the Countess of Chester Hospital in England are faced with a cluster of deaths in the neonatology department in 2015. The deaths are unexpected for the doctors, and they think they see a pattern: the then 25-year-old nurse Lucy Letby always seems to be present when things go wrong. They wonder if she might have a hand in it.
 
More deaths occur in the following months, and Letby is suspended. In 2016, the healthcare inspectorate concludes that there was no malicious intent behind the deaths. However, the inspectorate did find that the ward suffers from chronic understaffing.
 
This report is not sufficient for the doctors. They maintain that the nurse played a part in the babies’ deaths and take their suspicions to the police, who launch an investigation. In the following years, Letby is arrested and questioned several times. In November 2020, she is officially charged.
 
It is only in August 2023, after years in pre-trial detention and a 10-month trial, that she is finally convicted of murdering seven babies and attempting to murder six more. In a follow-up case earlier this year, she receives another conviction for attempted murder. A commission rejects her request for an appeal. The judge rules that the nurse will have to die in prison: she is given 14 life sentences.
 
This is a miscarriage of justice, says Leiden statistician Richard Gill, who was previously involved in the acquittals of nurses Lucia de Berk and the Italian Daniela Poggiali. Both nurses were found to have been convicted on the basis of flawed statistics. ‘I was one of four academics independently blogging on the Letby case’, he says. ‘We soon realised that the case seemed to be moving towards a questionable conviction.’

2. A SUSPICIOUS SCHEDULE

Just as with the acquitted nurses, the questions start with a schedule that supposedly shows how Letby was always present when something suspicious occurred. That schedule, which was presented to the jury on the very first day, is a table listing 25 deaths and so-called collapses (in which babies lost consciousness) during the period Letby worked at the hospital.
 
Each row in the schedule is a suspicious case and each column represents a nurse. If a nurse was present at a suspicious case, a cross is marked. Letby is the only one who has a cross marked for all suspicious cases.
 
According to Gill, the fact that those 25 specific cases were singled out and listed on the schedule is a sign that doctors started looking at incidents related to Letby with a huge confirmation bias: they only found what they wanted to find.
 
‘Any statistician will immediately wonder why, when and by whom it was decided that specifically those 25 incidents were considered suspicious. Because there were more deaths than those listed on that schedule, but no one seems to know exactly how many. If a child dies within the first six days after birth, English hospitals classify this as a stillbirth in other cases. That’s better for the hospital’s statistics, because these stillbirths don’t count towards mortality rates, so they don’t appear on this schedule either.’
 
Several newspapers are currently speculating that there were between six and nine other deaths that were not considered during the trial.
 
According to Gill, the doctors’ bias is apparent in several ways: ‘How did they arrive at these 25 cases? They argue that Lucy is present every time something suspicious happens, but the deaths are only considered suspicious because Lucy was present. Moreover, it’s bizarre that only nurses are included in this schedule. Why weren’t doctors or cleaning staff considered in the investigation? They assumed from the start that it was a nurse because they already had their eye on Letby.’

Another statistical blunder: all nurses are treated as equal in the schedule. ‘However, some work part-time, or they only spend part of the year working at that hospital. So they’re simply not there as much. Letby, on the other hand, worked a lot of overtime; she was in the hospital about 40 per cent of the time. You’re naturally going to see more deaths if you work so much.
 
‘Some of the nurses didn’t work night shifts, which are riskier hours because no doctors are present. But Letby did. In addition, not all of them have the same level of training, while Letby was one of the more experienced nurses on the ward. Therefore, it’s plausible that she would tend to look after the more vulnerable patients; patients with a higher risk of death.’
 
Furthermore, not all of the deaths were independent incidents, Gill notes. Several children on the list are twins, and there is one set of triplets. If one of them dies, it is more likely that the others are also at a higher risk. If you happen to be working when a seriously ill pair of twins comes in, you’re more likely to have two deaths occur during your shift. ‘This schedule omits a huge number of confounding factors that explain why Letby has so many crosses under her name without there being any malicious intent.’

3. CORONER VERSUS EXPERT

At the time, all the deaths were classified as natural by a coroner. It was only years later that an external police expert flagged them as suspicious: allegedly, there were indications that Letby had killed the children by means of insulin poisoning and injecting air into their blood vessels, causing air embolism.
 
Gill is adamant: ‘They concluded that Letby was guilty based on their prejudices. The police expert then made up a story about how those babies could have been killed, ignoring all other evidence.’
 
According to the statistician, everything points to the idea that it was easier for the doctors to think there was one malicious person on the ward than to face the fact that the ward was suffering from systemic failure, as previously suggested by the inspection report.
 
During the trial, a plumber testified that he had to visit the ward almost every week because sewage water was coming up from toilets and sinks on a regular basis, and because sewage pipes in the ceiling above the ward were leaking: a major infection risk for the prematurely-born babies on the ward, some of whom weighed less than a kilo. All the more reason to believe the children died due to inadequate care rather than a crime, says Gill.

4. THE GAGGING ORDER

The reason why critics have not previously challenged the questionable evidence has to do with the British jury trial system, in which the press is only allowed to report what is said in court during a case. Criticising or speculating on the prosecution’s plea is prohibited, as it could influence the jury and jeopardise the course of the proceedings.
 
Instead, the British press was all too eager in embracing the prosecution’s plea, complete with sensational headlines. As a result, ‘the monster Letby’ was soon cemented in the public mind.
 
As a British citizen subject to English law himself, Gill was also confronted with the fact that experts were not allowed to publicly express their opinions on the case. After writing multiple blogs about the case and sending a letter with statistical insights to the court, he was visited by the Dutch police late at night. ‘They found it very amusing that they had to deliver a letter from the British police to me.’
 
The contents of the letter were less amusing. If Gill did not stop publicly commenting on the case, he could be arrested on British territory. Should it turn out that his statements had influenced the jury, he would have to cover the costs of the entire trial. As a precaution, Gill waited until the end of the case before making further statements.

5. THE SHIFT

Now that the trial is over and Gill and other sceptical colleagues are free to voice their criticism again, there seems to be a gradual shift in the public perception of the nurse. For example, the British newspaper The Guardian revealed that a note presented by the prosecution as a confession by Letby had been written in the context of therapy.
 
Experts from other fields are also speaking out. A growing number of doctors and pathologists are expressing doubts about the medical evidence. For example, the test that served as evidence of insulin poisoning was allegedly incapable of measuring whether insulin had been artificially administered. In addition, the author of the article on air embolisms that was cited in the trial stated that, based on the evidence, there was no indication that the children had actually died from air embolisms.
 
Despite her life sentence, there remains a possibility that Letby could be released. Last week, it was reported that she has hired a new lawyer who will file a request to reopen the case with the court.
 
Gill is convinced of Letby’s innocence. Without the statistical evidence from the schedule and with the new criticism of the medical evidence, he believes little remains of the case: ‘There were at least five nurses on the ward at the time of each alleged murder, but there are zero eyewitnesses who saw her harm a child.’
 
Based on the figures, he concludes that no murders were committed at all. ‘During the years in which Letby allegedly murdered the children, mortality rates spiked in all hospitals in the region. The Countess of Chester Hospital wasn’t even an outlier. The whole case is a terrible blunder on the part of the healthcare system. If Letby is ever released, this could become one of the biggest scandals in British medical history.’