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Searching For the Evidence

Updated: Oct 14, 2023

Guest post by Mick Harper, Science on Trial community member Most of us are unfamiliar with the intricacies of statistics and this can lead to errors when unmasking serial killers. For example, if profiling has been used when seeking out a serial killer living among a population of a million non-serial killers, it is perfectly possible for a single person to be identified who meets all the criteria. Does this mean that person is the serial killer? Of course not, and no court would convict him (serial killers are overwhelmingly male) on such evidence.

However, police are people too. They may draw the understandable conclusion they have found their man and set about piecing together the evidence that will convict him in court. This in turn is a fraught procedure because evidence can be twisted (quite properly, we are not dealing here with so-called ‘noble-cause corruption’) to read one way when really it should be read another. When someone in court utters the fateful words — and someone always does — “It’s a million to one, the accused did the crime,” the accused is likely to be going away for a very long time.

Mostly this is right and proper. Sometimes it isn’t. In the Letby case there was a further difficulty: were there any crimes committed at all? Letby told the court that she believed consultants were pinning the blame on her, to cover up hospital failings — the strain of the workload, and at times unhygienic conditions in the nursery rooms. “There were often plumbing issues within the unit,” Letby said, saying “raw sewage” had been known to flow onto the floor, while out-of-service sinks left staff unable to properly wash their hands.

She would say that, wouldn’t she? Though to be fair, a lot of people have been saying a lot worse about a whole host of National Health hospitals.

Lucy Letby worked in the neonatal unit of The Countess of Chester hospital from 2009 until 2016. A neonatal unit is where babies that are premature or otherwise not routine births are cared for. It can be

expected to have a higher mortality rate than an ordinary maternity ward, though still not high.



















Table 1: Deaths at CoCH

Figure 1. Infant Mortality Rate at CocH showed a relationship between stillbirths and neonatal deaths

It was at this point that two things happened

  1. Letby was moved from the neonatal unit

  2. The Countess of Chester stopped providing care for premature babies

As a result the figures afterwards are not comparable. Despite this, doctors were

swift to claim that any problems identified by the increase in deaths in 2015–16 stopped when Letby’s role was switched.

When dealing with such small numbers — the Countess of Chester’s neonatal unit cared for some four hundred babies in an average year — it is difficult, perhaps impossible, to say whether such variations are normal or abnormal. For instance, it could be argued that the 2015 figure was skewed by the death of two triplets, the event that first triggered the investigation of Letby. In hospitals people are dying all the time, mortality spikes are happening all the time, serial killers are responsible almost none of the time.

When doctors and hospital administrators are faced with spikes they do not say — and nor should they say — “Oh, it’s our turn to have a spike.”They investigate. Oftentimes the spike is put down to normal variation, less often it is found there is a shortcoming that needs addressing. The real mischief comes with:

“Is it a serial killer? If so, who is in the frame?”

In hospitals these can be difficult questions to answer. Even in the close confines of a neonatal unit the number of people that have access is extensive. Notably, every nurse in the unit. The pattern of shifts and rotas in an NHS hospital mean every one of its neonatal nurses will likely be caring for all the babies at one time or another. The number comes down rapidly should investigators start going through one particular nurse’s attendance records, looking for any suspicious deaths, and discovering all of them occurred to babies under her care at one time

or another.

Now it was just a question of gathering the evidence. The problem was there was no evidence.

Every baby had been signed off as dying from natural causes, after a rigorous examination but no postmortem. The precise cause of death recorded at the time were ones that affect babies in neonatal units. The prosecution turned this to their advantage by listing the ways Letby could have murdered the seven babies without leaving a trace, creating the unfortunate impression that that’s how she did it.

The real evidence, the evidence that convicted a serial killer, was the material found in Letby’s home. She was that rare kind of serial killer, the one who keeps all the evidence of their crimes in loving detail. Not as trophies but as post-it notes and text messages.

Source: Radford University/FGCU Serial Killer Database

Perhaps we are all just an examination of our messaging habits away from prosecution for something or other. If you are on holiday, for instance, confine yourself to sending ‘wish you were here’ postcards to work colleagues. Do not send a text such as “I’ll be back with a bang” because you might be accused of ‘being out of control’.

If someone is sick do not enquire after them because, should that person die, you

might be accused of ‘playing God’. If they are all added up they might say at your trial something along the lines,

“Those texts give a sinister insight into Letby’s frame of mind.”

Never take work home. “In total, 257 confidential medical documents were recovered from Letby’s home.” That is a lot. One a fortnight over an eight-year career. Is that what over-conscientious nurses do, or is it what serial-killer nurses do? None of them were missed so they couldn’t have been very important. On the contrary, said the prosecution, “Many related to the babies she had hurt or killed.” Well, yes, all two hundred and fifty-seven documents related to babies under Letby’s care — she was doing no other kind of work — so many would relate to the

seventeen babies Letby was accused of harming or murdering. It would be grounds for suspicion if they didn’t.

Do not take your emotions home either. Make sure not to keep an indelible record if you do, they may be used against you Facebook data revealed Letby repeatedly searched for her victims’ parents. This included on Christmas Day, or on the anniversaries of the infants’ deaths. ‘Repeatedly searched’ implies obsessive behaviour though I think they mean she looked up each address once but there were seven sets of parents. Do not try to disguise your fell purpose by adopting anodyne sentiments.

Letby sent a sympathy card to the parents of one of her victims. She photographed it on her mobile phone hours before the victim’s funeral. The card read:

“Thinking of you today and always — sorry I cannot be there to say goodbye.”

Hours before! There is a window for these things. Though in truth nothing could save Letby once the wheels of justice had started turning.

In May 2017, Paul Hughes, a senior investigating officer at Cheshire Constabulary, was asked by his head of crime to look into a letter they had received from their local hospital. The Countess of Chester was concerned about a sudden spike in unexpected, and unexplained, deaths of the youngest patients in its care. But that was not quite all he was told.

Hughes met two of the consultants, Stephen Brearey and Ravi Jayaram, to ask what this meant. He was told when an infant collapses it’s usually explainable, and nearly always, expected. “They mentioned that a member of staff had been moved and that it coincided with no more collapses and no more deaths,” he said. Detective Superintendent Hughes didn’t get where he was by taking the word of civilians, no matter how eminent. He was by no means convinced Letby was a suspect. If another staff member was the culprit, they might have stopped when Letby was moved, to shift the blame. Besides, there was nothing to indicate

these deaths weren’t the result of natural causes — an infection or virus within the hospital for instance.

However Hughes was confident he was the man for the job:

“I made the parents a promise that we would investigate to find out the ‘what, when, why and how’ happened to each baby.”

And he was as good as his word. The police began to examine in detail the deaths of seventeen babies and the non-fatal collapses of sixteen more, some of whom had been left with life-changing injuries. They were the cases the doctors had selected from Letby’s workload which was most helpful. We all assume that for most problems there are experts ‘out there’ to solve them. But there are caveats when it comes to experts. They have a tendency to:

  • treat problems in terms of their own expertise

  • confirm conclusions known to have been arrived at by colleagues

  • resist being judged by experts from other fields of expertise,

which is only to say that experts are human.

Source: Radford University/FGCU Serial Killer Database

Nevertheless, it is worth bearing these things in mind as we watch the investigation unfold. Tens of thousands of medical files were prepared for a neonatologist — an expert in young infants — found via the National Crime Agency. In December 2017, their expert came back with his response. “These deaths were not the result of natural causes.” Operation Hummingbird had begun. From a strict statistical point of view there are two flaws here

  1. The person who received the files did not select the files. This is sometimes vulgarly referred to as ‘garbage in, garbage out’ but anyway is not the recommended procedure when drawing overall conclusions.

  2. That person already knew what general conclusion they were being asked to either confirm or reject.

A neonatologist does not ordinarily have tens of thousands of files dumped on his desk with the instruction, “What do you make of these?” More experts were called in, and they all said the same thing: a number of these deaths were not the result of natural causes.

In Britain, infant deaths are mercifully few, so experts are also few and, it would be fair to say, expertise is not extensive. But it was enough. The dye was cast, in all probability a serial killer was at work. It was now only a matter of identifying him or her. For the next few months, police teams spent hours analysing the shift and rota patterns of all the staff who worked on the Countess of Chester’s neonatal unit. The breakthrough came when they spotted a “concerning” pattern of behaviour. Among the hundreds of hours staff spent with the sickest of children, one thing was consistent. Nurse Lucy Letby was on shift, and usually alone, with the infants prior to their collapse.

“She was the thread running through them all,” Det Supt Hughes said.

This is quite untrue. The police had been told at the outset who the prime suspect was and police officers have neither the propensity nor the resources to do a proper ‘blind’ trial. If they had, they would have found it was not Lucy Letby that provided ‘the thread running through them all’, the thread ran through all the nurses at the Countess of Chester’s neonatal unit:

  • babies in neonatal units are by definition ‘the sickest of children’ which is why they typically spend days and weeks in neonatal units being cared for by full-time specialist neonatal nurses,

  • the number of babies are few and they require ongoing rather than intensive care which is why, in the always cash-strapped NHS, neonatal units have only one nurse on duty a lot of the time

  • that lone nurse will undoubtedly have been looking after a baby ‘prior to its collapse’, should that happen.

Nurse Letby ended up drawing the short straw so it is time to find out how those straws took her, and her alone, to prison.

It is not contested that Letby was suspected, investigated, tried and convicted largely on what might be called ‘guilt by association’. Here’s a question you might care to ponder:

Which nurse in the Countess of Chester hospital was associated with most cases of newborn babies developing serious or fatal conditions in the period 2012–16?

Lucy Letby started working in the neonatal unit of the Countess of Chester Hospital in January 2012, just before her 22nd birthday. On the surface, she seemed just like any other young nurse who loved her job. Her life seemingly revolved around the hospital. She lived nearby and would sign-up for shifts at short notice. Opinions about Nurse Letby were mixed Outside of work, she went to bars, restaurants and salsa classes with friends and colleagues.

When the local paper in Chester wrote a story about the unit, Letby was the member of staff chosen to hold up a tiny babygrow, alongside a short profile. “I enjoy seeing babies progress and supporting their families.”

“I would describe her as a beige individual,”
Nicola Evans, a deputy senior investigating officer

But underneath that veneer of normality, Letby was “devious, cold- blooded and calculated,” said Pascale Jones, a lawyer from the Crown Prosecution Service who helped bring the case against the nurse. “Behind that angelic smile there was a much darker side to her personality.” In the modern National Health Service it is safer to be an agency nurse.

Source: Radford University/FGCU Serial Killer Database

Following Letby’s arrest, thousands of pieces of "evidence" were prepared for her trial. Though, few have questioned what many came to deem as the the star exhibit; the green post-it note which was found in her house and where she had covered both front and back with a frantic scrawl reading:

“I don’t deserve to live. I killed them on purpose because I’m not good enough to care for them..."

A post-it note, that was the best evidence the prosecution could offer to tie Lucy Letby to the deaths of the babies under her care. Few people have stopped to wonder why when sitting one's own home they would right all over the front and back of a post-it, especially when she was not short of writing paper. Likewise, we do not know when it was written, or even the context upon which she wrote the note. The police initially claimed it was from 2016, but there is no evidence to support this claim.

In their recent documentary Cheshire Constabulary did reveal on piece of information related to obtaining Lucy's notes.

“We knew that she would write a lot, we’d seen it during the first arrest. So we wanted to arrest her and see what she’s been writing.”

This is what one of the police officers said in the Letby case. The statement suggests that Cheshire Constabulary were expecting to find notes after the intital 2018 arrest. One could be forgiven for speculating whether the post-it notes were actually written in Lucy's home. Could it be that the police observed her writing these notes over the three days she was held for questioning in 2018?

We shall not know, but there are few reasons as to why someone would write on the front and back of a post-it if they are sitting at home writing, surrounded by paper.


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Has this article been fact checked?

😳 Was there a NEONATOLOGIST found via the National Crime Agency — that we sent the cases and found the deaths to be murders?? Is this the truth? 😳

Why are we being told in the news that it was a retired paediatrician (who had been kicked out of a court by a judge for making up evidence) who sent an email to the police touting for the job, that reviewed the deaths and claimed alleged murders? - Not a neonatologis!?!

- Please tell me the truth. And adjust the information in the article so it won’t be false and misleading.

- Also, was there not 6/7 deaths post-mortem exams that showed the…

Replying to

"Rather than go to the police, Mr Harvey invited the Royal College of Paediatrics and Child Heath (RCPCH) to review the neonatal unit's service level. They visited the hospital in September that year.

In October 2016 Mr Harvey also contacted Dr Jane Hawdon, a premature baby specialist at the Royal Free Hospital, and asked her to review the case notes of babies who had died on the neonatal unit."

"Dr Hawdon produced what the BBC described as "a highly caveated report", writing that it was "intended to inform discussion and learning, and would not necessarily be upheld in a coroner's court or court of law".

She also recommended that four of the baby deaths be forensically investigated.

In a…


She wrote on ONE side of the post-it note NOT both sides.

5th paragraph: “Lucy Letby worked in the neonatal unit of The Countess of Chester hospital from 2009 until 2016”

---She began working as a registered nurse at unit in 2012. I think she also did a trainee work placement there during 2011 as a student nurse.

6th paragraph: The Countess of Chester did not "stop providing care for premature babies”

---On July 7, 2016 the neonatal unit was downgraded from a level 2 unit to a level 1 - i.e.

the gestational age limit of premature babies cared for was raised from 27 weeks to 32 weeks (and the number of cot spaces was reduced from 16 to…


Such a good, concise, sensible piece of prose which is just on the limit of words for a professional to take away and place into the mainstream, or a courtroom. Hope someone is collecting the best from SOT, like this, for such a purpose.


Sarrita Adams
Sarrita Adams
Oct 14, 2023

Please note: I have slightly modified this post, I was cautioned that it is somewhat outside the mission of Science on Trial, and it previously engaged in language that seemed to advance a viewpoint that was not clearly in alignment with SoT goals. The modifications occur at the end and removed some of the language that was adopted by the media.

Bruce Evans
Bruce Evans
Oct 16, 2023
Replying to

Maybe the Oswald nuance is just a little bit irrelevant here and, sixty years after the event, not a little lost on a lot of people. In communicating well it matters less what you say but more what is heard…as Mary has demonstrated well.


My understanding is that the retired non neonatal, non pathologist, non forensic scientist Dr Evans, who is prone to wild exaggeration such as ‘the tiny baby projectile vomited all over the nursery, all over the nursery…’, received 32 cases to review not ‘tens of thousands‘, sounds like another wild exaggeration.

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