Colin Norris was jailed for life in 2008 for the murder of four patients and the attempted killing of a fifth at hospitals in Leeds.
During his sentencing the 38-year-old was described by a judge as “a thoroughly evil and dangerous man”, yet he has always denied the killings.
But now Paul Moffitt, a juror in the case, has said the so-called Angel of Death should never have been found guilty.
He told the BBC that if the case was presented today with new scientific evidence that has recently emerged, he doubted if it would get to court.
Glasgow-born Norris was jailed for life in March 2008 after a five month trial, during which he was accused of injecting elderly patients with fatal doses of insulin.
A blood test from one of the women, Ethel Hall, had found more than 12 levels the normal level of insulin in her system.
But a BBC Panorama investigation in December raised the possibility that all of Norris’s victims could have died from natural causes.
In the documentary, one expert said another explanation for the abnormal blood result could be a rare condition called insulin auto immune syndrome (IAS).
According to the programme, IAS was said by prosecution experts at the trial to be too rare to be considered a possible explanation, but more cases have emerged since 2008.
The Criminal Cases Review Commission is considering whether the case merits an appeal.
Mr Moffitt, 36, who is the second juror to cast doubt on the conviction, said the new evidence showed that the nurse was not a killer.
“If this case was presented with this new evidence today, I don’t even know how it could possibly get to court in the first place,” he said.
“The evidence shows that a murder wasn’t committed at all, never mind four or one attempted murder, that’s what it shows to me.”
He added: “I’d like to see Colin Norris freed. That’s why I came forward, put my name forward, I just felt it would be my duty to do that.”
By Bill Gardner