It's thought to be the first major United Kingdom police investigation into child deaths in hospitals in 30 years, after nurse Beverley Allitt, nicknamed the Angel of Death, was jailed for 30 years for murdering four children with lethal injections.
She also had a placement at Liverpool Women's Hospital on Merseyside, which yesterday announced that it was involved in the police investigation and was reviewing patients who attended the hospital during her time there.
The probe is part of a lengthy investigation into a higher-than-expected baby mortality rate at the hospital.
"This is an extremely hard time for all the families and it is important to remember that, at the heart of this, there are a number of bereaved families seeking answers as to what happened to their children".
"Parents of all the babies continue to be kept fully updated and are being supported throughout the process by specially trained officers", the spokesman said.
Dr Anthony McCarthy of SPUC commented, "This distressing case, following on from what has recently been revealed about practices in Gosport, reminds us that the deaths of babies and vulnerable adults need to be given special attention".
Initially focusing on the deaths of 15 babies between June 2015 and June 2016, the investigation has now widened to a total of 17 baby deaths and 15 non-fatal collapses.
Officers arrived at the nurse's home in Chester on Tuesday and police were also seen at her parent's property in Hereford later that day.
Countess of Chester Hospital medical director Ian Harvey said the hospital was continuing to support an ongoing police investigation.
A second British hospital has been included in a police investigation examining the deaths of babies.
Hughes called the investigation "highly complex and very sensitive" and said his detective team was doing "everything we possibly can to try to establish in detail what has led to these baby deaths and collapses".
He added: "This is an extremely hard time for all the families and it is important to remember that, at the heart of this, there are a number of bereaved families seeking answers as to what happened to their children".
Ms Letby was even the face of a campaign to raise £3 million for the unit, and said at the time: 'I enjoy seeing them progress and supporting their families'.
Letby undertook a work placement at LWH after graduating in 2011.
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