A healthcare worker was arrested on Tuesday morning and taken into custody by police in the UK on suspicion of murdering eight babies and attempting to kill a further six. This is the first police investigation into child deaths in hospitals in nearly 30 years.

Police launched an investigation into the deaths of 15 babies and six non-fatal collapses at the women and children’s unit of the Countess of Chester hospital between June 2015 and June 2016. The force said on Tuesday the inquiry had widened to cover the deaths of 17 babies and 15 non-fatal collapses between March 2015 and July 2016.

Prosecutions of healthcare workers are rare and frequently difficult. Barrister Anthony Haycroft told the Guardian newspaper proving intent was crucial. In the Countess of Chester case, he said the police “will be looking first of all at the intent and if there was an intention to kill, it is murder. If it is a dangerous act irrespective of any intent, it is gross negligence manslaughter. In both cases, there has to be causation – for the actual death there must be a connection between the medical act and the death.”