Britain has been shocked by a horrifying announcement from police that a health-care worker has been arrested on suspicion of murdering eight babies and attempting to kill six more at a neonatal unit.

The breakthrough from police comes over a year after they began investigating the ward at the Countess of Chester Hospital in Cheshire, England, following serious concerns raised by the deaths of 17 babies and 15 “non-fatal collapses” between March 2016 and July 2016.

The hospital, based in the small city of Chester in the northwest of England, asked health investigators and police to investigate the potentially suspicious deaths last year. Police in Cheshire said the unidentified female health-care worker was arrested Tuesday morning and has now been placed in custody.

Detective Inspector Paul Hughes, who is leading the investigation, said in a statement: “Whilst this is a significant step forward in our enquiries, it is important to remember that the investigation is very much active and ongoing at this stage. There are no set timescales for this coming to a conclusion but we remain committed to carrying out a thorough investigation as soon as possible.”

According to The Guardian, police have updated all the families who were affected by the suspected baby murders and they are being offered support by specialist officers. Hughes went on: “This is an extremely difficult 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.”

The detective added: “At this stage we are unable to go into any further details about the investigation, but as soon as we are able to provide any further updates we will do.”

In November 2016, a damning report from the Royal College of Pediatrics and Child Health, known as the RCPCH, said there was a “higher than usual” number of baby deaths at the unit. It said there were “significant gaps in both medical and nursing rotas” and that the process for investigating infant deaths had to be strengthened.

The report also said that there was no “definitive causal correlation” between all of the potentially inexplicable deaths.

A spokesman for the hospital declined to comment to the BBC on whether any staff had been suspended in the wake of the arrest and police would not reveal the exact role of the “health-care professional.”

Medical Director Ian Harvey responded to news of the arrest with a statement to local media saying the hospital was continuing to support Cheshire police with the investigation.

“Asking the police to look into this was not something we did lightly, but we need to do everything we can to understand what has happened here and get the answers we and the families so desperately want.”

He added: “The Countess is now equivalent to a level 1 Special Care Baby Unit and we are confident the unit is safe to continue in its current form.”

Police are appealing to the public for further information.