Police are continuing to question a male nurse over the murder of three patients at the Stepping Hill Hospital in Stockport, Cheshire.
Greater Manchester Police arrested 46-year-old Victorino Chua on Thursday on suspicion of tampering with medical records. Detectives have since gained a warrant of further detention and are now questioning him on suspicion of three counts of murder and multiple counts of causing grievous bodily harm.
The patients - Tracey Arden, Arnold Lancaster and Derek Weaver - are believed to have had their saline drips contaminated sometime between June and July last year, causing hypoglycaemic episodes that led to their deaths. Police believe 21 patients in total were deliberately poisoned.
"Firstly, and most importantly, I must stress that we have not established the degree to which deliberate contamination of products may have contributed to the death of four patients," said Assistant Chief Constable Terry Sweeney.
"We have taken the decision to arrest this man on suspicion of murder in close consultation with the CPS, and it is important that no one jumps to any conclusions because of these steps or second guesses where our investigations will take us."
"We know that the victims and their families want answers. We are acutely aware of this and are working very closely with them, as well as hospital staff and the local community, to minimise the upset caused and to keep them fully updated of any and all developments."
In July, 27-year-old nurse Rebecca Leighton was arrested on suspicion of murder. She was released from prison in September after a police investigation found a lack of evidence.