A man was fighting for his life tonight at a hospital where police are already investigating the suspicious deaths of three patients.
Police fear the suspect who sabotaged saline containers with insulin may still be stalking the corridors of Stepping Hill Hospital in Stockport, Cheshire.
The critically-ill patient, a man in his 40s, is part of a complex police investigation with 60 detectives questioning more than 50 staff at the hospital, with wards A1 and A3 the centre of the investigation.
Police have a "working assumption" that the contamination had taken place within the hospital and officers said they could not rule out the person responsible still being at the hospital but it may also be a visitor to the site.
The unexplained deaths of Tracey Arden, 44, George Keep, 84, and Arnold Lancaster, 71, are all being linked to the deliberate contamination of the saline solution.
They are among a total of 14 patients whose treatment since July 7 is being examined by police.
Detectives were called in after an experienced nurse reported a higher than normal number of patients on her ward with "unexplained" low blood sugar levels pointing to the saline ampoules being sabotaged.
Officers found insulin had contaminated a batch of 36 saline ampoules in a storeroom close to ward A1 of the hospital.
The three deaths remain unexplained as detectives await the results of further pathology tests to find out if the insulin contributed to fatality.
Inquests into the deaths of all three victims were opened and adjourned by South Manchester Coroner John Pollard today.
Chris Burke, chief executive of Stockport NHS Foundation Trust, said: "Our staff are shocked, horrified and angry at what's happened.
"They are alarmed that a place that should be for care has become a crime scene.
"This is a criminal act, perpetrated by someone with malicious intent. We do not believe it could have been anticipated.
"This is about someone wanting to inflict harm, pain and, possibly further, as a deliberate malicious act. That is nothing to do with care."
Security had been ramped up and there are now daily review meetings between senior police and NHS bosses.
Greater Manchester Police Assistant Chief Constable Ian Hopkins told reporters that "at the moment" the investigation was concentrating on the 14 patients in total who may have come to harm.
He said: "At that stage, when we have got a clear suspect we are dealing with, is the time we will look at historic deaths."
Mr Hopkins said officers were questioning a large number of people and had a large amount of forensic evidence to sift.
He added: "With this being a complex investigation, it is unlikely there will be very early arrests.
"Our investigation in the initial stages is concerned with people who work or visit the hospital.
"We are not ruling out it could be someone outside the hospital, but our focus is on staff and visitors to the hospital."
James Catania, medical director at Stepping Hill, said insulin was always kept in a refrigerator in a locked treatment room.
Saline solutions were now also being kept in a locked room.
He said saline drips were "technically benign products" which the hospital used in "hundreds and thousands on a daily basis".
Medics were now working in pairs to check and administer drugs across the hospital.
Bosses had also brought in rules so a single key holder has to be asked for access to locked drugs cabinets and names and times were being taken each time drugs were given to patients.