After a fifth patient died at a British hospital where detectives fear saline solution was deliberately contaminated with insulin, police questioned a 27-year-old nurse on Friday.
Police arrested Rebecca Leighton Wednesday on suspicion of murder over the deaths of three patients given the contaminated solution at Stepping Hill Hospital in Stockport, outside Manchester in northwest England.
Police believe someone deliberately tampered with a batch of saline and nine other patients may also have been affected. One of them, a 41-year-old man, has been described as being in a critically ill condition.
Investigators will also be reviewing previous deaths at the hospital for any evidence of foul play.
"I can confirm that there have been two further deaths that we are linking to the investigation into deliberate contamination of medical products," Greater Manchester Police Assistant Chief Constable Ian Hopkins told reporters.
An 83-year-old man had died earlier Thursday, while an 84-year-old woman had died on July 14, he said. Her case was referred to the police following medical procedures.
Police were Thursday granted an extension to detain Leighton until 2005 GMT on Friday. She was arrested at her home on Wednesday. Officers removed bags of items from her flat.
"This is a complex investigation and we are awaiting the results of medical tests to confirm the causes of death of all those that we are currently investigating."
Detectives have always linked the deaths of a 44-year-old woman and two men aged 84 and 71 to the contamination.
Hopkins said they were now awaiting the results of post mortems on the two latest deaths.
"These are complex medical investigations that take time. At this stage we have no information as to what the exact cause is," he said.
"Our focus at the moment is about preventing any further harm to patients within the hospital, and the investigation to bring to justice the person who has committed these deliberate acts."
But detectives would also look back at previous deaths at the hospital, he added.
"Once we've achieved those two aims then we will look historically at cases prior to July 7."
Police were called in last week after a nurse reported a higher than normal number of patients on her ward with "unexplained" low blood sugar levels, pointing to saline ampoules being sabotaged.
Officers found insulin had contaminated a batch of 36 saline ampoules in a hospital store room.
At the hospital, medics are working in pairs to check and administer drugs.
Rules have been changed so a single key holder has to be asked for access to locked drugs cabinets and names and times are being taken each time drugs are given to patients.