A Hells Angels hitman convicted of first-degree murder more than a decade ago has won a new trial.

Dean Kelsie was charged in the killing of Sean Simmons, who was gunned down in the lobby of an apartment building on Trinity Avenue in Dartmouth on Oct. 3, 2000. At Kelsie's trial, the jury heard evidence that Simmons was killed because he allegedly had an affair with the wife of a Hells Angel.

Kelsie was convicted in March 2003 on both murder and conspiracy to commit murder. He was ordered to serve a minimum of 25 years before he could begin applying for parole.

Kelsie filed notice of his intent to appeal five days after he was convicted. It's not clear why it took 13 years for his case to land before the Nova Scotia Court of Appeal.

In a decision released today, the Court of Appeal said the original trial judge made a mistake when he failed to leave manslaughter as an option when giving his final instructions to the jury.

"In my view, the trial judge erroneously eliminated manslaughter as a verdict, which was available on a characterization of the evidence in Kelsie's statement," Justice David Farrar wrote for the three-member panel.

The court also had problems with instructions that the trial judge, Justice Felix Cacchione, gave the jury on the first-degree murder charge.

"The trial judge's error goes directly to the mens rea requirement for an aider to a first-degree murder," Justice Farrar wrote.

"It was not a minor error; to the contrary, it is fundamental to a finding of guilt for first-degree murder."

In trying to keep the conviction intact, the Crown pointed to the "overwhelming" evidence against Kelsie.

Much of the case against him relied on the testimony of two police informants, the husband and wife team of Paul Derry and Tina Potts. Both had extensive criminal records of their own.

"When considering the broader context of this trial, to say that the people involved, including Derry and Potts, were unsavoury characters would be an understatement," the court wrote.

"It would be extremely dangerous to rely on the evidence of Derry and Potts to conclude the case against the appellant was overwhelming. I would decline to do so."