WARNING: Readers might find the details in this story distressing.
It began with a blunt message for anyone doubting the guilt of the UK's most prolific child killer in modern times.
"All of this noise has caused enormous additional distress to the parents who have already suffered far too much," Lady Justice Kathryn Thirlwall said in her opening statement on Tuesday.
That "noise" is the growing chorus of voices questioning Lucy Letby's convictions. They've popped up in various places over the past few months — including the media and a letter to government ministers.
But on Tuesday, Justice Thirlwall, a senior Court of Appeal judge, made it clear she wasn't buying in to what she described as an "outpouring of comment".
"I make it absolutely clear that it's not for me, as chair of this public inquiry, to set about reviewing the convictions," she told the inquiry at Liverpool Town Hall.
"The Court of Appeal has done that with a very clear result. The convictions stand."
And there's a lot of convictions.
Letby is serving multiple life sentences in prison after last year being found guilty of murdering seven infants and attempting to kill seven more between June 2015 and June 2016.
The inquiry will probe the Countess of Chester Hospital — where Letby worked as a nurse — and specifically examine whether management was too slow to identify it had a serial killer in its ranks.
The fact Lady Justice Thirlwall even referenced the "noise", shows how much there is.
In a letter sent to government ministers in July, a group of 24 experts warned the probe shouldn't ignore the possibility Letby didn't murder the babies. They contended the infants could have died as a result of hospital negligence or other factors.
Scepticism of Letby's convictions gained global attention following the publication of a May article by The New Yorker — which helped thrust the case in front of a new audience — questioning the 34-year-old's guilt.
While Letby is a household name in the UK, with her mugshot adorning the front pages of newspapers and being splashed across TV news bulletins, her crimes are less known abroad.
Lady Justice Thirlwall on Tuesday told the inquiry that the questions about Letby's guilt had come almost exclusively from people who did not attend the former nurse's 10-month trial.
The judge also rejected calls for the scope of her inquiry to be broadened.
'Missed opportunities' to stop baby killer
On the first day of evidence, the inquiry heard there were a series of "missed opportunities" to prevent Letby from murdering and harming babies and that the hospital failed to investigate a cluster of unexpected deaths, despite staff describing them as shocking and odd.
Counsel assisting the inquiry Rachel Langdale KC told the hearing that doctors found the process of reviewing child deaths at the Countess of Chester Hospital to be "desperate and inconsistent" and that one senior doctor "deeply regrets" not escalating his concerns about Letby sooner.
The inquiry was told there had been a divide between doctors and nurses over whether Letby should be removed from her duties on the neonatal ward once concerns about her possible involvement in the unexpected deaths had been raised.
"My recollection is that the clinicians became more vociferous about [Letby] being removed, while the nurses wanted her to remain," then hospital medical director Ian Harvey said in his statement to the inquiry.
"It was difficult at this stage to understand what the issue or issues were and whether it might relate to her competency or performance, or was completely unrelated to her practice."
The inquiry was told Mr Harvey had been advised by the hospital's director of corporate and legal services, Stephen Cross, to contact police about the cluster of deaths in June 2016. However, police were not notified until April 2017, almost two years after Letby's killing spree is thought to have begun.
"[In 2016] contacting the police was discussed, however, the decision of the senior managers appears to have been not to approach the police at this stage, but rather to commission reviews in the neonatal unit and inquire into the circumstances of the deaths on the unit," Ms Langdale told the inquiry.
Over the coming months, the inquiry will hear testimony from the parents of Letby's victims, as well as doctors, nurses and managers who worked with Letby at the Countess of Chester Hospital.
A report outlying the inquiry's findings is expected to be released next year.
Doubts over Letby's guilt building
Despite Lady Justice Thirlwall's warning that months of rising speculation over the validity of Letby's convictions has caused distress to the families of her victims, a small but adamant group of medical experts and statisticians are pushing for the evidence used in her trials to be re-examined.
Those raising doubts claim some evidence used in Letby's trials was flawed, including a spreadsheet that showed Letby was the only nurse on shift for all suspicious deaths between June 2015 and June 2016.
"That spreadsheet is an example of the famous phrase 'lies, damned lies and statistics' because it is a damned, lying statistic; it's utterly misleading," said Richard Gill, a professor of mathematics at Leiden University, who spoke to the ABC ahead of the inquiry.
The spreadsheet produced by the prosecution shows which nursing staff were on duty during 25 suspicious deaths or baby collapses in the neonatal ward. Letby is the only name with an X in every box.
"You could ask, 'where are the doctors, and where are the technicians and the cleaning people?', they've all been left out [of the spreadsheet]," Professor Gill said.
"What should have been done would have been to have expanded the spreadsheet with all the other people who were moving about on the unit."
Other deaths on the neonatal ward during that time period were also absent from the spreadsheet."This was a textbook example of an investigation driven by confirmation bias, it has become completely clear that is the case," Professor Gill claimed.
The spreadsheet is just one example of data some statisticians like Professor Gill say was wrongly presented to convict Letby.
Many of their criticisms formed the basis of Letby's two appeal attempts, which were denied.
In a 58-page ruling, the appeal court judges earlier this year said the handling of the trial had been "thoughtful, fair, comprehensive and correct".
Letby has exhausted the appeal options open to her, but is instructing a new legal team to put her claims to the Criminal Cases Review Commission, which has the power to send cases back to the courts.
Professor Gill has previously helped free two other nurses who had been found guilty of murdering patients from prisons in the Netherlands and Italy.
The prosecution's case in Letby's original 10-month trial included the testimony of six expert medical witnesses, thousands of documents, blood test results, X-rays and handwritten notes by Letby including one that read "I killed them on purpose because I'm not good enough".
Prosecutors claimed Letby used various methods to kill her infant victims, including injecting air into their bloodstreams and poisoning them with insulin.
During the trial, doctors at the hospital gave evidence that they raised concerns about Letby eight months before she was removed from the neonatal unit, but claim management dismissed them.
Letby gave evidence during her trial that the hospital was rundown, and that she was being used as a scapegoat to cover up deaths that happened for other reasons.
Letby was convicted without forensic evidence linking her to the deaths, or witnesses who directly saw her kill the children.
The case instead relied on the cumulative effect of many different pieces of circumstantial evidence that, when put together, convinced a jury to convict her of numerous murders, after more than 110 hours of deliberations.
Criminal psychologist Dr David Holmes said in medical cases like Letby's, circumstantial evidence was often the only form of proof available.
"Circumstantial evidence should not be dismissed, particularly in these cases where the circumstantial evidence is massive," Dr Holmes told the ABC in an interview conducted before Tuesday's inquiry began.
"In these particular cases, often it's this circumstantial evidence that mounts up and mounts up until you are 99.99 per cent certain this person had to do this, there is no one else, it has to be this person who has actually committed a crime because this baby has died, this baby should not have died, there are no other circumstances under which this baby could have died, therefore, someone has actually intervened and you are the only person who was there at the time.
"This analysis is far more significant than one piece of absolute significant CCTV video or eyewitness testimony."
During her criminal trial, Letby faced a total of 22 charges — seven counts of murder and 15 counts of attempted murder relating to 17 babies in total.
She was not found guilty of all charges.
Letby was convicted of killing seven babies and trying to kill six others.
She was found not guilty on two other counts of attempted murder and the jury failed to reach a verdict on a further six counts of attempted murder.
The Thirlwall Inquiry was established by the government last year and is expected to last at least four months.
