The key medical witness in the Lucy Letby trial passed 25 further suspicious incidents to police but no further action was taken, it has emerged.
In an interview with The Telegraph, Dr Dewi Evans said that following Letby's conviction last August he went back over all 82 medical files given to him by the police and found further cases of concern.
The paediatrician, 75, said he had stopped working on the Operation Hummingbird investigation into Letby and was no longer licenced to practise, so did not know why there had been no further action taken.
Letby was convicted of the murder of seven infants and the attempted murder of seven others at the Countess of Chester Hospital between 2015 and 2016.
Dr Evans was the expert who initially evaluated the medical files of babies from the hospital after consultants had raised concerns that babies were dying under Letby's care.
"Following the verdict, I wrote to Cheshire Police last September and said 'look, I've only done preliminary reports on these, but I think they need to be looked at in more detail'.
"And I just listed 25 cases of mine, and it might be that nothing comes of any of them. For instance, I found one baby where there was a displaced breathing tube. Well, you can't prove anything without one displaced breathing tube, but if that breathing tube was displaced and there was no obvious reason for it, then you might become a bit worried.
"And then there are other babies who suddenly became seriously ill with an infection. Okay, premature babies are always at risk of infection. So, there were other concerning cases."
Since the verdict, many neonatologists, scientists, statisticians and medics have voiced their concerns about the case, claiming that the evidence shown to the jury was flawed. The defence called no expert witnesses in the case.
At a meeting of the Royal Statistical Society earlier this month, it was claimed that the shift pattern data was 'scientifically worthless'
Statisticians said there were "issues with the selection and collection of data" used in the chart and warned there may be "many other possible causal factors not being considered that might explain these deaths".
Dr Evans said: "They are right, statistics were worthless in the Letby trial. The evidence had nothing to do with statistics. Sadly their understanding of medicine and law is even less than lawyers' and medics' understanding of statistics.
"If the prosecution felt that statistics were relevant they presumably would have obtained an opinion from a statistician. They didn't. And if the defence thought that the prosecution was somehow misinterpreting statistics they would have obtained an opinion from a statistician. They didn't."
Dr Evans said he had invited experts who disagreed with him to get in touch. "Give them my email and we can have a chat about it. I'm not holding my breath."
Cheshire Police are continuing to investigate incidents, including unexpected collapses at Liverpool Women's Hospital where Letby did two work placements in 2012 and 2015.
Dr Dewi Evans is annoyed. The key prosecution witness in the case of Lucy Letby has faced a barrage of criticism and has even been reported to the General Medical Council since the trial of the nurse concluded.
Letby was convicted of the murders of seven infants and the attempted murders of seven more and Dr Evans said he was left with no doubt that she wrought "carnage" on the wards of the Countess of Chester Hospital between 2015 and 2016.
Yet in recent months, an unprecedented stream of neonatologists, scientists, statisticians and medical staff have come forward to question the evidence presented to the jury.
They argue that a shift pattern chart - which showed Letby had been present at each baby death or collapse - was statistically flawed and that there were other explanations for high death rates at the hospital, such as suboptimal care and sicker, smaller babies.
Dr Evans is unconvinced.
"I really am quite annoyed with statisticians," he told The Telegraph. "I think they've not been very professional. It never crossed my mind, or the police's or the prosecution's or anybody's, that statistics were relevant.
"The chart was used simply to show that Letby was present at the scene of the crime.
"They say the chart only showed those cases where she was present. What about the deaths that were not part of the trial? Well, if you did that, it wouldn't help the prosecution or the defence, because for the other deaths, she was actually present for most of them when the baby died.
"But those babies died of one or other of what causes deaths in babies. So four babies had an infection and were premature, four babies had multiple congenital abnormalities. One baby had severe brain damage. He was transferred and died elsewhere."
Critics of the case have argued that the death rate at the Countess of Chester was abnormally high even when allowing for the Letby deaths. While two or three deaths a year were usual for the neonatal unit, there were 17 linked to the unit, of which Letby was only charged with seven.
Dr Evans confirmed that 10 deaths had never been put before the jury because they lacked the "key consistencies" that suggested foul play. To make it onto the charge sheet, the deaths had to be "unexpected" and "unexplained" by conditions which affect babies, such as infection, sepsis or a congenital problem.
"There were issues with all of those seven (babies) that were suspicious, "he added "Why has this baby collapsed? That's suspicious. Babies don't do that suddenly.
"Why have these babies not responded to resuscitation? That in itself is suspicious.
"What is most surprising was the comments from neonatologists who should know better, because they were commenting on cases where they've not seen the clinical records, they've not been in court."
Outside experts have pointed to problems on the ward which could have raised the risk of death for the babies. The unit was understaffed, cramped and taking more vulnerable babies than usual. Since the trial, it has also emerged that the neonatal unit was plagued by an outbreak of pseudomonas, a bacterium known to be lethal to vulnerable babies.
At the Thirlwall Inquiry, which is currently looking at how the deaths could have been prevented, parents of the babies who died have spoken of unhygienic practices on the unit, and described scenes of 'chaos' and 'pandemonium'.
One father told the hearing how he had caught doctors and nurses Googling how to carry out a life-saving procedure, and described the hospital's operating theatre "like something out of a horror film".
The year before the Letby deaths, a premature baby had died after doctors mistakenly put a breathing tube in his gullet when it should have gone into his trachea. Several of the babies also experienced medical accidents while on the ward including four incidents where umbilical venous catheters (UVCs) were placed wrongly or fell out.
However, Dr Evans believes concerns about the hospital have been overstated.
"I think that the criticism of the Chester unit as dysfunctional is inappropriate," he said.
"Before Letby started her carnage, the survival rates of even the smallest babies in Chester were very good, just as good as the Office of National Statistics figures for England and Wales.
"There were protocols for all sorts of things, which is not something you'd get in a dysfunctional unit. When the babies collapsed, the consultants were there. And then the evidence that the nurses and the doctors gave (at the trial) clearly they knew what they were doing.
"I didn't know about the case of the baby whose team went into the oesophagus instead of the trachea. That's unfortunate. Sadly, this could have happened anyway. That's not trying to defend it."
A former paediatrician from Carmarthen, Dr Evans, 75, retired from practising medicine in 2009, setting up a company called Dewi Evans Paediatric Consulting providing expert medical advice in legal matters such as child abuse cases and criminal trials.
In 2017, just a month after the first report had been made to Cheshire Police, Dr Evans read about the investigation in the local paper and sent an email to the National Crime Agency, which read: "If the Chester Police have no one in mind I'd be happy to help. Sounds like my kind of case."
He had already worked on 49 cases for the NCA and was sent thousands of pages of unredacted medical notes from the Countess of Chester.
Although Letby's name may have appeared in the files, Dr Evans said he did not notice the nurse while reviewing the cases and had no contact with the doctors who had accused her of harming babies in her care.
"I knew nothing," he said. "None of the names registered with me. I had never been to the hospital, didn't know the medical staff, or spoken to any of them. I've still not been in touch with any of the medical staff, or any of the nursing staff."
After being invited to review some of the deaths on the neonatal ward, it was Dr Evans who suggested the possibility of air embolism as a cause of death in some of the babies even though post-mortems had largely concluded the deaths were natural or unascertained
Asked why air embolism had been missed on the post-mortems, Dr Evans said: "You will not find an abnormality on post-mortem if the death is a result of air injected into the circulation.
"Quite frankly, I expected the pathologists to be called (to give evidence) in the same way that the paediatricians were called.
"The defence barrister spent an awful lot of time arguing medical facts with medics. That's not going to end well."
Letby was sentenced to 15 whole life sentences, meaning that, unless she has the convictions overturned on appeal, she will be in prison for the rest of her life. But Dr Evans believes there may be more cases to come.
Although he is no longer working with Operation Hummingbird - the investigation into Letby - he passed a further 25 "suspicious" files onto the police last September.
"It might be that nothing comes of any of them. For instance, I found one baby where there was a displaced breathing tube," he said.
"Well, you can't prove anything without one displaced breathing tube, but if that breathing tube was displaced and there was no obvious reason for it, then you might become a bit worried, you know.
"There were other concerning cases but my kids have been increasingly paternalistic about their old dad, and they think I should be stopping."
Cheshire Police are continuing to investigate incidents, including unexpected collapses at Liverpool Women's Hospital where Letby did two work placements in 2012 and 2015.
At the Thirlwall Inquiry, Richard Baker KC, representing the families of 12 babies, said that the Liverpool hospital had conducted an audit and found breathing tubes had become dislodged on 40 per cent of shifts Letby worked.
"It is unusual, and you will hear that it occurs generally in less than one per cent of shifts," said Mr Baker at the hearing.
Dr Evans is dubious about the one per cent claims, telling The Telegraph that "seems very low".
"It could be of no significance at all," he said. "If it's 30 tubes in six months, and she happened to be there 40 per cent of the time, I would dismiss it. But if it's 30 tubes in six months and they've excluded the known causes of displaced tubes, then that's very concerning.
"It would be interesting to calculate probability, looking at the incidence of tube displacement in relation to the cause. For once one would benefit from a statistician's input."