Former nurse Colin Norris may appeal against his murder conviction based on new evidence provided by a leading expert on insulin and hypoglycaemia.
A television documentary, to be screened tonight, is understood to include evidence calling into doubt the conviction. It is to be passed to the Criminal Case Review Commission.
Mr Norris was convicted in 2008 by Newcastle crown court of the murder of four patients at Leeds General Infirmary by insulin poisoning, and the attempted murder of a fifth.
He was jailed for life and told he would serve a minimum of 30 years. He was also struck off the nursing register in April 2009.
In December 2009 he lost an appeal against his convictions with three judges ruling that the conviction was “safe” and the case against him “very strong indeed”.
However, an investigation by BBC Scotland suggests the deaths may not necessarily have been murder.
Police began investigating when Ethel Hall died after suffering an unexplained episode of hypoglycaemia, before finding another four cases in which patients had also suffered unexplained hypoglycemic episodes.
Mr Norris had been on shift for each incident and in the trial the prosecution argued that a cluster of five hypoglycemic cases was so rare that it must mean foul play.
But Professor Vincent Marks, a world renowned insulin expert, told the BBC that up to 10% of older patients in hospital experience the condition, apparently contradicting the prosecution’s argument.
Professor Marks reviewed all relevant research on the subject carried out since 2008, and found that a cluster of hypoglycemic comas in non-diabetics was not unusual.
He said: “I was surprised at how very common it is in this particular group of elderly, sick people. In one very detailed survey, of thousands of patients, it was up to 10%. In others it was 5% and so I thought, well, you know, it’s not that rare after all.”
Asked if it would be unusual for a cluster of four or five patients to occur in a period of a year, he told the BBC: “It wouldn’t be unusual if you were looking through a hospital that had several thousand people over the age of 70 who are sick and so on, over the course of a year – not at all.”
Mr Norris’ lawyers are understood to be considering an appeal application, based on the evidence revealed in the documentary.
Stockport nurse Rebecca Leighton was last month cleared of the murder of three patients amid allegations that saline solution was tampered with. Police investigations are ongoing.
The programme BBC Scotland Investigates: Hospital Serial Killer – A Jury In The Dark will be broadcast on Tuesday at 10.35pm, and will be available elsewhere online.