The Supreme Court of Canada has upheld a new trial for Gordon Dwight Hurley in a slaying at a Lloydminster motel in October 2005. (CBC)

An Alberta truck driver should be retried in the slaying of a Saskatchewan woman, says the Supreme Court of Canada.

In a ruling Friday, the top court agreed with a Saskatchewan Court of Appeal decision that Gordon Dwight Hurley should be retried in the killing of Jarita Naistus.

Naistus's body was found in a Lloydminster motel room in October 2005. She had been strangled and beaten.

Hurley was convicted of second-degree murder in 2007 and sentenced to life in prison. But he appealed the conviction, arguing, among other things, that the trial judge made a mistake by failing to sufficiently warn jurors about the potential motives of a key Crown witness.

The witness was Darrel Niemi, who shared a jail cell with Hurley and later informed on him to police, saying Hurley spoke about the case in jail and admitted wiping the homicide scene of DNA evidence. Niemi, who was facing unrelated charges of his own, testified against Hurley in court.

Saskatchewan's Court of Appeal agreed that the trial judge erred and quashed Hurley’s conviction in 2009, ordering a new trial. The Crown appealed that ruling to the Supreme Court of Canada.

But the Supreme Court on Friday sided with Saskatchewan's top judges and agreed Hurley should have a new trial.

"Mr. Niemi's evidence … failed to flag … his knowledge of a [police] reward [for information leading to a conviction] and the fact he was in custody and facing charges at the time," the Supreme Court said in its written decision.

At the time of his trial in 2007, the Crown had DNA evidence linking Hurley to the scene of the crime, and more DNA linking him to the scene was found later.

Additional DNA, also not available at the original trial, belonged to a third person, raising the possibility that someone had been in the motel room with Naistus after Hurley left, the Supreme Court noted.

"The new evidence, coupled with the evidence of someone else’s DNA on a cigarette butt inside the Bacardi Breezer bottle, may have had an impact on the outcome of the trial in the following three ways," the Supreme Court said in its decision.

"It could have led to the conclusion that Mr. Hurley was not the last person in the room with Ms. Naistus; it could have cast doubt on the Crown’s theory that the room was cleaned or an attempt was made to clean DNA and fingerprints out of the room, which in turn could have cast doubt on the credibility of Mr. Niemi; and it could have bolstered the credibility of one of the civilian witnesses who testified she saw Ms. Naistus with persons other than Mr. Hurley on the evening Ms. Naistus was killed."

Hurley's Saskatoon lawyer, Morris Bodnar, said he would like to see the new trial start in the fall. Hurley, from Beaverlodge, Alta., remains in custody, but might apply for bail. Bodnar said the Supreme Court ruling is important.

"The public should care [about the case], because they could be the next ones identified by a jailhouse informant when they know nothing about a crime, and they could be spending four years in custody not having committed something," Bodnar said.