Police investigating suspicious deaths at a hospital say they are working flat-out, with 60 detectives on the case.
Ian Hopkins, Assistant Chief Constable of Greater Manchester Police, said the thoughts of officers were with the family of Tracey Arden, 44, George Keep, 84, and Arnold Lancaster, 71, who died at Stepping Hill Hospital in Stockport.
The deaths of all three are being linked to the deliberate contamination of saline solution, with the hospital now at the centre of an intense police investigation.
Insulin was found in a batch of 36 saline ampoules in a storeroom close to ward A1 of the hospital in Stockport, Cheshire.
Detectives believe the insulin was deliberately injected into the saline containers which were used in drips by at least two wards, but they say the three deaths remain unexplained as they await post-mortem examination results.
Mr Hopkins said: "Our thoughts continue to be with the families of Tracey Arden, George Keep and Arnold Lancaster. The anguish they will be feeling at this time must be terrible.
"I would like to reassure them we are doing all we can to find out what caused the death of their loved ones.
"There is an ongoing complex investigation requiring detailed forensic analysis and we are continuing to interview a large number of witnesses.
"We have about 60 experienced detectives working on this. They have worked 24/7 since the investigation began and they working as fast as they can without compromising the quality of the investigation.
"We recognise this is an incredibly difficult time for staff at Stepping Hill Hospital who are dedicated to the care of people and saving life.
"We are working closely with hospital managers to minimise disruption to the running of the hospital, but ultimately our duty is to those who have died and their families to conduct a thorough investigation into their deaths.
"We are also working to reduce the risk of harm to others being cared for at Stepping Hill."
The family of Mr Keep said they fear more patient deaths will be investigated.
A patient with lung cancer, Mr Keep died at Stepping Hill Hospital two days after a ward nurse raised concerns about a higher than normal number of patients with unexplained low blood sugar levels.
The pensioner from Cheadle was admitted to Stepping Hill on June 27 after he suffered a broken hip in a fall.
He was operated on and was recovering well until two days before his death when his blood pressure and blood sugar levels started to drop, said his daughter Carolyn Knowles.
She said her family were now "concerned" that the number of deaths that police are investigating will rise.
"If you go into hospital, it is supposed to be a safe place," she said. "It is a place where you trust people.
"You just don't possibly imagine anything like this could possibly happen. I just cannot imagine anyone wanting to do that to someone else.
Her husband David added: "If the police start looking into the past, they might find all sorts of awful things and that doesn't bear thinking about."
Greater Manchester Police's major incident team is focusing its investigation from July 7 onwards, but will review previous deaths at the hospital if new information comes to light.
Long-term multiple sclerosis sufferer Ms Arden, a mother-of-two, died on July 7, while Mr Lancaster died last Monday.
There has been growing speculation that several more deaths may be looked at and that the contamination could have taken place outside the hospital.
Police are continuing to interview doctors, nurses, porters, patients and visitors, while security remains high in and around the hospital.
Eleven people who survived the effects of the tampered medication will also be interviewed.
South Manchester coroner John Pollard is due to open inquests on all three deaths tomorrow.
All future deaths at the hospital that show any signs of relevant symptoms will be passed to Mr Pollard for the foreseeable future and may be referred to detectives to investigate.
Ms Arden, of Heaviley, Stockport, was admitted from her care home for routine drug treatment for her MS.
Her parents Keith and June visited her in the afternoon but were later called back by the hospital as she had "taken a turn for the worse".
By the time they arrived, their daughter, who had been in care since she was diagnosed with MS at the age of 32, was already dead.
Ms Arden's brother Gary said: "During the afternoon my mother and father had been to visit her, then they left her looking like she was recovering well. Colour was coming back into her cheeks and so on, she was responding well to her treatment.
"They left and then a relatively short while afterwards they received a call from the hospital that Tracey had taken a turn for the worse and they think they should come on and see her.
"By the time my mother and father arrived, she had just passed away."
He said his parents left the hospital at 4pm and Ms Arden died at about 6pm.