The case of a nurse who was was jailed for life for murdering four patients and attempting to kill a fifth has been referred to the Court of Appeal.
Colin Norris, 38, was convicted in 2008 of injecting the patients with insulin in hospitals in Leeds.
The Criminal Cases Review Commission said new evidence created a “real possibility” his conviction was unsafe.
BBC Scotland and Panorama investigations had previously cast doubt on the verdicts.
Norris, who was originally from Glasgow, was convicted of murdering Doris Ludlam, 80, Bridget Bourke, 88, Irene Crookes, 79, and 86-year-old Ethel Hall.
He was alleged to have injected them with lethal doses of insulin at Leeds General Infirmary and the city’s St James’s Hospital in 2002.
He was also found guilty of attempting to murder 90-year-old Vera Wilby.
All five women were elderly inpatients on orthopaedic wards where Norris worked as a nurse.
The CCRC said its decision followed a detailed review of what it described as a “complex and difficult case”.
It noted the case against Norris, who was jailed for a minimum of 30 years, was “wholly circumstantial” and “heavily reliant on expert opinion evidence”
As a result of new expert evidence, the CCRC said: “There is a real possibility that the Court of Appeal will decide that that Mr Norris’s conviction for the murder / attempted murder of one or more of the four patients is unsafe.”
In the case of Mrs Hall it said the conviction depends upon support from the other four cases that “no-one other than Mr Norris could have been responsible”.
It concludes: “In light of the new expert evidence, the CCRC is satisfied that this assertion is now less secure and that, as a result, there is a real possibility that the Court of Appeal will quash this conviction too.”
BBC Scotland Investigations correspondent Mark Daly first reported his concerns about the conviction in 2011.
Norris’ case has also been championed for more than a decade by Inside Justice UK.
The campaign group said it was “thrilled” by the news, which was announced on Norris’ birthday.
The appeal was led by Michael Mansfield QC.
In 2015 the foreman of a jury which convicted Norris told the BBC he now believes the man is innocent.
Paul Moffitt spoke out after a Panorama investigation suggested the women may have died of natural causes.
He told the BBC that if the case was presented today with the new evidence, he doubted if it would get to court.