Colin Norris, 38, was jailed for life in 2008 for murdering four patients and attempting to kill a fifth while working at Leeds General Infirmary and the city’s St James’s Hospital in 2002.
Juror Paul Moffitt spoke out after an investigation by Panorama for the BBC suggested the women may have died of natural causes.
He told the Corporation that if the case was presented today with the new evidence, he doubted if it would get to court.
Norris, from Glasgow, notoriously labelled the Angel of Death, was convicted at Newcastle Crown Court in 2008 following a five month-long trial.
He was convicted of murdering Doris Ludlam, 80, Bridget Bourke, 88, Irene Crookes, 79, and 86-year-old Ethel Hall and attempting to murder 90-year-old Vera Wilby. Prosecutors said Norris injected the woman with lethal doses of insulin.
In December’s BBC Panorama programme, Prof Terry Wilkin, an endocrinologist from the University of Exeter, Dr Adel Ismail, a retired clinical biochemist, and insulin poisoning expert Prof Vincent Mark all challenged the prosecution case with a series of claims.
Juror Paul Moffitt told the BBC that new evidence presented by the programme showed the nurse was not a killer. He is the second juror to cast doubt on the conviction.
He said: “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.”