Letby has been found guilty of murdering seven babies and of seven counts of attempted murder.

She was also found not guilty of two attempted murder charges, while the jury could not reach verdicts on six further counts of attempted murder.

Cheshire police began looking into the deaths of babies at the neonatal unit of the Countess of Chester Hospital back in May 2017, in what became known as Operation Hummingbird.

Officers say they have examined more than half a million medical and digital records during the probe, which saw Letby charged in November 2020.

The 33-year-old stood trial accused of murdering seven babies and trying to murder 10 others at the hospital between June 2015 and July 2016. She always denied the charges.

Read more: Reaction after verdicts reached in Lucy Letby trial

Police say they have been supporting the victims' families, many of whom attended Manchester Crown Court in person during the nine-month trial.

Senior officers, as well as the Crown Prosecution Service (CPS), gave an update outside court following the announcement of the verdicts.

"Time and again she harmed babies in an environment that should have been safe for them," Pascale Jones, from the CPS, said.

She said Letby's actions were a "complete betrayal of the trust placed in her" and that Letby showed the families of her victims "fake compassion".

A police family liaison officer said justice had been done but the result was "bittersweet" as some families had not got the outcome they deserved.

Letby started working in the hospital's neonatal unit just before her 22nd birthday - around four years before the start of the allegations in the trial - and colleagues raised suspicions more than a year before bosses contacted the police.

Former Countess of Chester nurse Lynsey Artell said she fears that Letby attacked her son, Asa, who was on the hospital's neonatal ward after being born two months premature.

The boy's treatment by Letby was not the subject of any charge and Ms Artell is calling for the police to reinvestigate her claims and those of other parents.

Following the verdicts, Cheshire police confirmed they are now investigating whether Letby could have attacked other children in her care before June 2015.

Detective Superintendent Paul Hughes, the senior investigating officer in the case, said: "We're obviously committed to looking at the entire time that Lucy has been employed as a nurse, whether it's a unit at the Countess of Chester Hospital (or) the Liverpool Women's Hospital.

"That's to make sure that we, at the end of Operation Hummingbird, can say with a degree of confidence that we've investigated every baby."

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He could not say how many other active cases there are but added: "There are cases where we've told parents."

The probe will look into the other years Letby worked at the Countess of Chester, as well as time she spent on training placements at Liverpool Women's Hospital.

Sky News has contacted both hospitals for comment.

DCI Nicola Evans, the deputy senior investigating officer on the case, said: "I don't think there's anybody who has worked on this investigation who will come out of the other side the same person they were.

"It has been heartbreaking."