Six people believed to have been "deliberately poisoned with insulin" at Stepping Hill Hospital have now died, according to Greater Manchester Police.
John Beeley, 73, and Linda McDonagh, 60, are the latest people to be named by detectives investigating the suspicious deaths of patients at the health institution in Stockport.
Tracey Arden, 44, Arnold Lancaster, 71, Derek Weaver, 82, and William Dickson, 82, were also among 21 people believed to have been unlawfully administered insulin at Stepping Hill between June and July 2011.
All patients suffered hypoglycaemic episodes after saline drips were sabotaged.
Detectives believe only the deaths of Ms Arden, Mr Lancaster and Mr Weaver have direct links to insulin poisoning, with the remaining three deaths thought to be due to natural disease.
Detective Superintendent Simon Barraclough, of Greater Manchester Police, said: "It is really important that we differentiate between the deaths of Tracey Arden, Arnold Lancaster and Derek Weaver - who died shortly after being poisoned - and the three subsequent deaths.
"We believe insulin may have played more than a minimal part in the deaths of Tracy, Arnold and Derek.
"While we are continuing to undertake stringent tests into the deaths of all six patients, we believe that it is highly likely the later deaths should more properly be attributed to natural disease."
Mr Barraclough said a team of highly experienced experts is continuing to carry out comprehensive testing on the patients' bodies, with the process expected to take up to several more months to ensure results are "as certain as possible".
"It is only when these tests have been concluded that we will be able to say with authority how they died, based on expert scientific evidence," he added
Mr Beeley, who was known as Jack, died on Friday, while mother-of-three Mrs McDonagh died on January 14, police said.
The former NHS clinic administrator's devastated family said she was poisoned while battling with motor neurone disease and pneumonia last summer, but decided to turn off her non-invasive ventilator earlier this month because she had "had enough" of the crippling condition.
Husband Stewart McDonagh, 61, a car mechanic from Offerton, Stockport, said: "There's someone out there preying on vulnerable people while they should be in a place of safety.
"The person who's done this to my wife and other people should come forward and search their conscience."
Mr McDonagh said that his wife's blood sugar levels "dropped dramatically" when she was poisoned. When doctors removed the saline drip and replaced it with another, it "brought her back" and she recovered "within minutes", he said.
All deaths took place on wards A1, A2 or A3 - acute care wards caring for seriously ill patients.
Earlier this month, a 46-year-old male nurse suspected of murdering three Stepping Hill patients was released on police bail until April pending further inquiries.
Victorino Chua was arrested on suspicion of tampering with medical records and was further arrested on suspicion of three counts of murder and 18 counts of causing grievous bodily harm.
Fellow nurse Rebecca Leighton, 28, spent six weeks in jail following her arrest in the investigation.
She was released and cleared of any wrongdoing last September when prosecutors said there was not enough evidence against her.
Miss Leighton had been detained on suspicion of murder and later charged with damaging saline products.
Mr Chua and Miss Leighton are prevented from working at the hospital.
Police chiefs have previously stressed that detectives have not yet established the degree to which deliberate contamination of products might have contributed to the patients' deaths.
They added that about 650 people have been spoken to by officers since the contamination was discovered when nursing staff raised the alarm.