Leighton Hay was convicted of the first-degree murder of Colin Moore, 51, who was shot and killed in July 2002 at a Toronto nightclub where he was hosting a monthly fundraiser.
Hay has served about 10 years of a life sentence, and been in prison for more than a decade — mostly in the psychiatric wings of two Canadian penitentiaries.
In an unusual move, the Supreme Court considered new forensic evidence — hair samples that Hay's lawyers say prove his innocence.
In its unanimous 7-0 verdict, the court ruled a new trial is necessary to consider the fresh evidence.
"The fresh evidence that Mr. Hay seeks to admit could reasonably be expected to have affected the jury's verdict," wrote Justice Marshall Rothstein on behalf of the majority.
"The interests of justice require that the Court remit the matter for a new trial, in which the Crown would have the opportunity to adduce evidence challenging the reliability of the fresh evidence."
Gary Eunick and another man pumped eight bullets into Moore after he and his brother, Roger, sought shelter in the nightclub's kitchen.
It was their way of solving a dispute that erupted when Eunick and a group of men refused to pay a cover charge after arriving at the club a short time before, just after midnight.
Eunick and Hay were tried together and convicted.
While Eunick's identity was never in doubt, Hay was convicted as his accomplice on the testimony of one witness. The reliability of her evidence has now been called into question.
Hay's prosecutors also relied on hair found in a newspaper in his bathroom garbage, as well as hair in the electric razor on his nightstand.
The prosecutors argued that Hay had shaved his scalp to change his appearance after the shooting.
Hay's lawyers tested the hair and obtained expert opinions that said the samples did not, in fact, come from his scalp.
"Mr. Hay argues that the fresh evidence establishes that the hair clippings did not come from a shave of Mr. Hay's scalp and that, as a result, acquittal or a new trial is warranted," Rothstein wrote.
Friday's ruling overturns the Ontario Court of Appeal, which rejected Hay's appeal.
In another legal twist, one of the judges who rejected Hay's initial appeal was Michael Moldaver, who has since been appointed to the Supreme Court.
Moldaver was not involved in Friday's Supreme Court ruling.
Hay's lawyer, James Lockyer, said his client won't be a free man any time soon.
He said he will bring a bail application to have Hay transferred to a psychiatric hospital because he has serious mental disabilities and likely can't cope in the outside world.
"Leighton Hay is a highly vulnerable member of society," said Lockyer, the founder of the Association in Defence of the Wrongly Convicted, which has successfully exposed several wrongful convictions in Canada.
"That's what I'll be asking for in the court — that he be essentially given bail so he can move into a hospital."
Lockyer said Hay's father and sister were "over the moon," when they learned of the Supreme Court's decision in his Toronto office.
But Lockyer said he didn't actually think Hay was able to grasp what had happened when he reached his client inside Millhaven Penitentiary.
Lockyer also spoke to Hay's doctors, who told him his client described Friday's decision was "bad news," likely because he was unsure of how he would be able to replace his familiar routine outside prison walls.
"There's a framework to his existence," Lockyer explained.
Nevertheless, Lockyer said Hay's doctors were happy for him, something he doesn't typically see with other clients.
"They're all celebrating up in Millhaven, believe it or not."