Detectives arrested a 26-year-old nurse on suspicion of murder Wednesday over the deaths of three hospital patients given insulin-contaminated saline solution, police said.
The woman worked at Stepping Hill Hospital in Stockport, where police were alerted last week to a batch of saline believed to have been deliberately tampered with.
The unexplained deaths of a 44-year-old woman and two men aged 84 and 71 are being linked to the contamination, while a fourth patient, a man in his 40s, remains critically ill.
"This morning, a 26-year-old woman was arrested on suspicion of murder. She remains in police custody for questioning. Inquiries are continuing," a spokesman for Greater Manchester Police said.
A police source said the woman was a nurse.
In total, 11 out of 14 patients originally affected by the contamination have survived.
Hospital chief executive Chris Burke told a press conference Wednesday that staff were "shocked, horrified and angry" at the events.
"They are alarmed that a place that should be for care has become a crime scene," he said.
"This is a criminal act, perpetrated by someone with malicious intent. We do not believe it could have been anticipated.
Creative Commons image via flickr user hiitsthatwitch