A lawyer for convicted killer William Sandeson has argued that a detective hired by the defence before the murder trial but who later talked to police was a "traitor" and that the judge did not address the issue fairly.

Dalhousie student Taylor Samson, 22, was killed in August 2015 in an apartment in south-end Halifax. His body has never been found.

A jury convicted Sandeson, 27, a former Dalhousie medical student, of first-degree murder following an eight-week trial that ended in June 2017.

He is appealing that conviction. A hearing in the Nova Scotia Court of Appeal got underway Monday morning in a Halifax courtroom with Sandeson's lawyer Ian Smith asking for a new trial.

The CBC's Blair Rhodes liveblogged from court:

He focused much of his arguments on the issue of retired RCMP Sgt. Bruce Webb, who worked for a private detective agency hired by Sandeson's lawyers to help them prepare for the trial.

In the course of his work, Webb interviewed two men — Justin Blades and Pookiel McCabe — who were in the apartment across the hall from Sandeson and initially told police they didn't see or hear anything the night Samson was killed.

But when Webb pressed them, the men changed their story. They told Webb they saw a bleeding man slumped over the kitchen table in Sandeson's apartment.

Webb subsequently told a police officer that investigators should requestion Blades and McCabe, which they did.

It wasn't until in the middle of the trial that Sandeson's lawyers realized that Webb was the reason police reinterviewed Blades and McCabe.

Taylor Samson is seen on surveillance video outside the apartment of William Sandeson, the man convicted of killing him. (CBC)

The lawyers asked for a mistrial on the grounds that Webb's actions breached Sandeson's privileges as a client, but Nova Scotia Supreme Court Justice Josh Arnold refused.

Smith argued Arnold underestimated the seriousness of the detective's actions and its impact on the fairness of the legal process.

He said Arnold failed to ask himself whether Canadians would be shocked to learn a member of the defence became a "state agent" in the midst of an investigation.

"The defence had a traitor of the defence team... [Sandeson] was betrayed by someone with a duty to him," Smith told the three-member Appeal Court panel. "It was incumbent on the trial judge to consider all the factors."

Had police sought legal advice, Smith said they likely would have been told not to accept Webb's information. He argued it was a violation of the police's oath of office.

But Crown lawyer Jennifer MacLellan argued the defence was given adequate opportunity to address the issues with Webb.

Murder victim Taylor Samson, 22, was reported missing on Aug. 16, 2015. (Halifax Regional Police)

She pointed out that the name "Bruce" was referred to throughout the statements from the two witnesses ⁠— which were in the hands of the defence before the trial ⁠— and that it shouldn't have been a surprise to anyone that he was involved.

"We see the connection that should have made this absolutely apparent to [Sandeson's lawyer]," she said. "It's all over this that he was involved.

"You know what the easiest thing to do is here, you call up and the Crown and say, 'Who's Bruce?'"

She said the trial judge was in the best position to determine if there was a miscarriage and whether a mistrial was warranted.

But Justice David Farrar, a member of the Appeal Court panel, suggested Monday police had an obligation to defence to tell them what Webb had done.

"How can our system ever survive if we allow police to subvert the interest of justice?" he said.

MacLellan noted Arnold found that while the Crown failed to disclose the information in a timely fashion, there was no violation of litigation privilege. She agreed with those findings.

She also said Webb feared he could be charged with obstruction of justice if he failed to reveal to investigators that two Crown witnesses had lied in their earlier police statements.

Apartment search 'serious invasion of privacy'

Smith said another ground for appeal is that investigators conducted the search of Sandeson's south-end Halifax apartment without a warrant, claiming there were "exigent circumstances" which justified their actions.

Police said that at the time of the search, they were worried Samson was being held hostage as part of a drug deal gone bad.

But Smith argued there was no evidence Samson had been in the apartment and that the search was not lawful.

"They had only a hunch that Samson was present," he said. "The search of the home is a serious invasion of privacy."

Smith said after the initial search, police returned to the apartment to turn off a DVR Sandeson had been using as part of a surveillance system, fearing its contents could be erased remotely.

Smith argued there was no evidence to suggest that could happen, and there was no reasonable basis for returning to the apartment a second time.

Finding of 1st-degree murder 'unreasonable'

Smith claimed Sandeson's rights were violated by police as their investigation shifted from a missing persons case to a homicide.

Sandeson was initially arrested on a kidnapping charge, but Smith said the officer's aggressive line of questioning suggested he was suspected of murder.

He noted Sandeson is repeatedly referred to as a "monster." Sandeson said very little during the interrogations and asked for a lawyer, he said.

Smith also argued the finding of first-degree murder was unreasonable.

He said the Crown's theory that he planned the killing is possible, but so are the theories that he was simply planning a drug deal or a robbery.

"There's also strong evidence that there was no plan," said Smith, noting Sandeson identified his apartment in text messages and had items in his apartment that would identify him.

Two days have been set aside for the appeal hearing. MacLellan is expected to continuing making arguments on Tuesday.

Sandeson is currently serving a life sentence with no parole eligibility for 25 years.

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