Convicted killer nurse Lucy Letby faces more investigations as police reveal they are examining "the entirety of her employment" for other potential cases.
Cheshire Police say it is looking at her time at both the Countess of Chester Hospital and Liverpool Women's Hospital between 2012 and 2016.
Officers say it is "impossible to provide a figure" of cases they were working on, but said there had been more than 4,000 admissions during the time period.
Detective Superintendent Paul Hughes stressed that not every case was being investigated for possible criminality - but each was being reviewed "from a medical perspective" to ensure nothing had been missed.
He said: “From 2012 through to 2016, there were more than 4,000 admissions of babies into the neonatal units of both the Countess of Chester Hospital and the Liverpool Women’s Hospital for us to work through.
"This does not mean we are investigating all 4,000, it just means that we are committed to a thorough review of every admission from a medical perspective, to ensure that nothing is missed throughout the entirety of her employment as a nurse.
"Only those cases highlighted as concerning medically will be investigated further.”
He added: "The Operation Hummingbird Team is committed to a complete and thorough investigation into the full period of time that Lucy Letby was employed as a nurse, either while at the Countess of Chester Hospital or on placement at the Liverpool Women’s Hospital.
"This investigation remains ongoing, through a transparent and open-minded process.
"The families of all babies, who are part of this investigation, have been informed and are supported. We will of course provide a more detailed update when we can.”
Two experienced neonatologists are looking through the medical notes of children to identify in very broad terms any unexpected and unexplained collapses, he added.
He said if an issue is identified then it will be passed to the particular hospital to “overlay their knowledge” of the case before a decision is made on whether to take the matter any further.
Mr Hughes said: “We are not narrowing it down to Lucy Letby. So a doctor could say ‘I have a concern about a case here’ and she might not even have been there.
"It’s not specific to her because it would be too directive.”
Liverpool Women's Hospital has said it is investigating Letby's time working there whilst she was a student.
Liverpool Women's Hospital said: "There is an ongoing investigation relating to the full period of Lucy Letby’s career, including training placements at Liverpool Women’s Hospital, which took place between October – December 2012 and January – February 2015.
"Liverpool Women’s NHS Foundation Trust has been liaising with Cheshire Police throughout this investigation and we will continue to do so going forward.
"As this is an ongoing investigation, we are unable to provide any more information at this time. Any further details will be shared by Cheshire Police in due course."
The jury was undecided on the attempted murder of a further four babies.
She will be sentenced on Monday 21 August in Manchester.
In a statement read outside court, Detective Chief Inspector Nicola Evans, of Cheshire Constabulary, said: “All of their babies will forever be in our hearts. I would like to thank all of the families in this case for their exceptional resilience and strength throughout this entire investigation, their composure and their dignity during this trial have been truly overwhelming.
“The investigation into the circumstances surrounding this case started in May 2017, and since that time hundreds of witnesses have been spoken to by a team of dedicated detectives.
"Many of those witnesses have returned to court on numerous occasions to give evidence, without their honesty and their support the families would not have received the justice that they have received today.
“I cannot begin to imagine how the families in this case feel today, I just hope that today’s verdicts bring all of them some peace of mind for the future and that we have answered some of the questions that they were looking for.
“Cheshire Constabulary will continue to support all of the families in this case in the coming days and weeks ahead, there will be a period of reflection as everybody comes to terms with what they’ve experienced here today.”
An independent inquiry will also be held into Letby's case to examine “the circumstances surrounding the deaths and incidents, including how concerns raised by clinicians were dealt with”, the Department of Health said.
Dr Nigel Scawn, Medical Director at the Countess of Chester, said the Trust is committed to ensuring that 'lessons continue to be learned'.
He said: “We would like to extend our thanks to Cheshire Police for their extensive investigation and the work they did to bring this case to trial.
“We would also like to thank them for the comprehensive support that they have provided to all the families involved.
“Since Lucy Letby worked at our hospital, we have made significant changes to our services and I want to provide reassurance to every patient that may access our services that they can have confidence in the care that they will receive.
“Finally, and most importantly, our thoughts are with all the families and loved ones at this very difficult time.”
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know…