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A ´óÏó´«Ã½ Scotland investigation which will be broadcast tonight (Tuesday 4 October) reveals new evidence which could pave the way for the release of convicted serial killer, Colin Norris.

´óÏó´«Ã½ Scotland Investigates: Hospital Serial Killer – A Jury In The Dark (10.35pm, ´óÏó´«Ã½ One Scotland) reveals the findings of a world-renowned medical expert which cast doubt on the safety of the convictions.

Glasgow-born Colin Norris was dubbed the "Angel of Death" after he was found guilty of poisoning with insulin five elderly patients in his care at Leeds General Infirmary, murdering four of them.

The investigation by West Yorkshire Police began in November 2001 when pensioner Ethel Hall died after suffering an unexplained episode of hypoglycemia – when blood sugar falls to an extremely low level.

The police investigation started working backwards and produced another four cases in which the women involved had also suffered unexplained hypoglycemic episodes. They had all originally been certified as having died of natural causes.

The police learned that Colin 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 reporter Mark Daly tonight discloses new evidence from Professor Vincent Marks, the world's most experienced insulin expert, that up to 10% of elderly sick in hospital suffer this condition. The scientific findings contradict the prosecution argument that these cases were exceptionally rare.

Professor Marks undertook a forensic analysis of all the new international medical studies carried out since 2008 which he says disproves the belief – a key part of the prosecution case – that a cluster of hypoglycemic comas in non-diabetics was extraordinary.

Professor Marks tells the ´óÏó´«Ã½ Scotland programme: "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 replied: "Well, 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."

He told the programme he believes that using cases in the Colin Norris trial as evidence of insulin administration is unsafe.

Defence solicitor, Jim Littlehales, who was with Colin Norris throughout the police interviews, said: "The new evidence would blow, effectively, a very large hole in what was the central plank in the prosecution case."

Barrister Paul Williams, who represented Colin Norris during his trial, said: "The new scientific evidence is incredibly powerful indeed."

Among the boxes of material not used in evidence in the trial, the programme production team found the case of Lucy Rowell who had also developed hypoglycaemia and fell into a coma from which she did not recover.

Relatives told the programme the police had informed them that Lucy Rowell's death was being treated as suspicious and that Colin Norris was being investigated.

But her granddaughter Miranda Carpenter said around eleven months after police had said her grandmother's death may have been murder, they dropped the case.

She said: "They just told us that Colin wasn't working the night grandma slipped into the coma."

Solicitor Jeremy Moore, who has reviewed the trial papers, and has taken on Colin's case, said: "It seems that they trawled through hospital records looking for evidence of patients that might have died suspiciously but it seems they only cherry picked those cases when Colin was on duty and ignored any others that might have occurred in the hospital."

An application for an appeal, based on the new evidence revealed in the ´óÏó´«Ã½ Scotland documentary will be submitted to the Criminal Cases Review Commission.

´óÏó´«Ã½ Scotland Investigates: Hospital Serial Killer – A Jury in the Dark,10.35pm, ´óÏó´«Ã½ One Scotland

Viewers outside Scotland can access this programme on Sky Channel 971, Freesat Channel 960, Virgin Media Channel 862 or on ´óÏó´«Ã½ iPlayer .

The programme will also be shown on the ´óÏó´«Ã½ News Channel at 00.30 am, Wednesday 5 October.

JG2