The jurors have started their deliberations in the William Sandeson murder trial, but what they don't know is that the defence team tried to shut down the trial after their own private detective went behind their backs and pointed police to damning evidence.

​Sandeson is accused of killing Taylor Samson, a fellow Dalhousie University student, in August 2015. The prosecution has argued Sandeson faced money problems and lured Samson to his Halifax apartment on the pretext of doing a drug deal, and then shot him to death and stole his nine kilograms of marijuana.

The intrigue involving the detective can now be reported as the 12 jurors in the Halifax trial are cut off from outside contact as they deliberate whether Sandeson is guilty of first-degree murder.

Other details of the case that can now be published include how Sandeson allegedly threatened to dismember his girlfriend and dump her body on his family farm near Truro, N.S. — a threat made just weeks before he allegedly murdered Samson.

Defence sought mistrial

The defence's bid for a mistrial, which was rejected on the second-last day of trial by Nova Scotia Supreme Court Justice Josh Arnold, revolves around some of the most damning evidence the jury heard.

The testimony came from two people who were in the apartment across the hall from Sandeson's and heard a gunshot the night Samson was killed. Justin Blades and Pookiel McCabe also testified they saw a man slumped over in Sandeson's kitchen that night, bleeding to death.

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

But for 14 months following the killing, Blades and McCabe maintained they saw nothing. It was only as the defence was preparing for trial that the men changed their story.

The defence argued for a mistrial because of the actions of Bruce Webb, a retired RCMP sergeant — and now a private detective — who had been hired by Sandeson's legal team to track down and interview potential witnesses, including McCabe and Blades.

Both men had tried to drop out of sight, troubled by what they'd seen. But Webb tracked them down.

Witness afraid to come forward

When Webb talked to Blades at his Halifax home, Blades was extremely agitated but seemed relieved to finally tell his story. He explained that part of the reason he was afraid to come forward before was that he believed Sandeson had ties to the Hells Angels. Blades said Sandeson had implied as much when he talked about travelling to Montreal for drug deals.

The defence was able to argue successfully that mentioning the Hells Angels would be highly prejudicial to Sandeson's case, so the jury never heard that detail.

But the defence had a bigger problem with the testimony from Blades and McCabe: the Crown and police might never have learned their stories if Webb — hired by the defence — hadn't told them.

Webb testified at the mistrial voir dire without the jury in the courtroom.

"It appeared that Mr. Sandeson's case wasn't really good for him," Webb said. "I also felt that at that point, if I didn't come forward, I would be obstructing justice."

'Got the feeling he knew the accused was guilty'

Webb was working for Martin & Associates Investigations Inc., a firm of private detectives run by retired Halifax homicide detective Tom Martin. The firm had been hired by Sandeson's defence team to help prepare for the trial.

Webb has since been fired, court was told.

Police told court that they found several items inside Sandeson's safe, including a 9-mm Smith and Wesson handgun and a box of ammunition with two shells missing. (CBC)

The police officer he tipped off was Halifax Regional Police Staff Sgt. Richard Lane.

Lane lives in the same neighbourhood as Webb. Lane testified that one day in October 2016, he was out with his family's three-month-old puppy, walking along the side of the road.

A car pulled up. It was Webb. He told Lane that police investigators should go back to Blades and McCabe — who had already told police they saw nothing. Lane was too preoccupied with his puppy to say much to Webb, so he promised someone would be in touch.

"I got the feeling he knew the accused was guilty and didn't want him to get away with it," Lane testified.

Police say Sandeson's gun was found with one bullet in the chamber. (Court exhibit)

When investigators called Webb, he offered to facilitate a meeting with Blades. They met at Blades's home the next day. Webb made the introductions, then left.

The defence team claimed they didn't know their own private detective had reached out to police until the trial was well underway. They argued that the trial must be halted and a mistrial declared.

The judge disagreed and refused to declare a mistrial.

Threat to dismember girlfriend

As for the threat Sandeson is supposed to have made toward his girlfriend, Sonja Gashus, it was contained in text messages sent four to five weeks before the homicide.

In the texts, Sandeson was communicating with another woman. He told her he suspected Gashus was cheating on him. He told the woman that if he found out that was true, he'd put Gashus's head and hands in a bucket of lye and dump her body on the Sandeson family farm near Truro — the same farm that police would later search and find evidence related to the Samson homicide.

The court heard that this shower curtain was found on the Sandeson family farm. A DNA expert testified that Samson's blood was on it. (Court exhibit)

Lye is a caustic alkali that can be used to dissolve bodies.

This text message was never introduced at trial, but was revealed during Sandeson's bail hearing. The hearing was held in October 2015, two months after Samson disappeared.

At that hearing, Justice Jamie Campbell denied bail, saying Sandeson was "highly motivated to flee."

Sandeson "tends to tailor his answers to what he knew police had at the time," Campbell said in his decision.

Sandeson has been in custody since his arrest in August 2015.

Video evidence the jury didn't see

Another major piece of information withheld from the jury is the latter part of Sandeson's police interrogation.

The jury sat through hours of video of RCMP Const. Jody Allison cajoling and pleading with Sandeson to "do the right thing" and "man up." Sandeson was largely unmoved by the appeal.

Sandeson is seen on a video of his interrogation by police investigating the death of Samson. (CBC)

What the jury didn't see was the portion when Det. Const. Roger Sayer of Halifax Regional Police entered the room for the second time. By that point, police had collected evidence from Sandeson's apartment and his text messages.

When Sayer re-entered the interrogation room, he was loud and aggressive, repeatedly berating Sandeson, at one point calling him "a piece of shit."

The defence successfully argued that this video was highly prejudicial to Sandeson. The Crown had to edit the video of the interview to remove that section.

In this trial, there were a total of 10 voir dires — trials within a trial where the jury was sent out of the courtroom and lawyers proceeded to argue over issues and evidence. It is highly unusual to have this many interruptions during a trial. Usually, these issues are resolved in pre-trial conferences.