A woman in Chester, England, has been arrested on suspicion of murder in the deaths of eight babies, and the attempted murder of another six babies while working in the neonatal unit at Countess of Chester Hospital.

Authorities are investigating a total of 17 deaths that occurred at the hospital between March 2015 and July 2016, the London Evening Standard reports.

Investigators announced Tuesday that an unidentified woman, a healthcare worker, was arrested in connection with with the deaths, and that they are looking into another 15 incidents of “non-fatal collapses” of infants during the same timeframe, according to a press release by the Chester Constabulary.

The arrest follows a lengthy investigation by authorities, who said they’re “committed to carrying out a thorough investigation as soon as possible,” as the probe into the unfathomable case continues.

A cause in the babies’ deaths has not yet been revealed, with police citing the ongoing investigation.

“We recognize that this investigation has a huge impact on all of the families, staff and patients at the hospital as well as members of the public,” a statement by officials reads.

“Parents of all the babies are continuing to be kept fully updated and are being supported throughout the process by specially trained officers. 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.”

Though the suspect has yet to be identified, police did confirm that she is a healthcare professional. It is not known if she is a doctor or a nurse or has another position.

Anyone with information into the case is asked to email Operation Hummingbird at operation.hummingbird@cheshire.pnn.police.uk.

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