A former Dalhousie University medical student convicted of murdering a fellow student is suing the private detective hired to help his defence team but who instead tipped off Halifax police to incriminating evidence.

In documents filed in Nova Scotia Supreme Court, William Sandeson alleges Bruce Webb, along with his former employer Martin & Associates Investigations Inc. and its owner Tom Martin, failed in their fiduciary duty to him.

Sandeson was found guilty by a jury last year of first-degree murder for killing Taylor Samson in August 2015. He is serving a life sentence with no parole eligibility for 25 years.

The Crown's theory at trial was that Sandeson set up a drug deal with Samson and then shot him to death in order to steal his nine kilograms of marijuana. Samson's body has never been found.

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Two of Sandeson's neighbours, Justin Blades and Pookiel McCabe, testified at trial about hearing a loud noise coming from Sandeson's Halifax apartment the night Samson disappeared.

The pair got a glimpse inside the apartment moments later. They told the court about seeing a man slumped over at the kitchen table, a pool of blood forming at his feet and money scattered on the floor.

The dramatic testimony was one of the key moments of the trial. But Sandeson argues it should never have happened.

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In their initial statement to police, both men had claimed they saw and heard nothing that night.

In preparation for trial, Sandeson's lawyer, Eugene Tan, hired Martin & Associates to interview prospective witnesses. Martin dispatched Webb, a retired RCMP officer, to track down Blades and McCabe.

While they'd withheld information from police, they opened up to Webb. The pair said they had been afraid to tell the truth because they believed Sandeson had ties to the Hells Angels.

Webb in turn alerted a neighbour, Halifax Regional Police Supt. Richard Lane, that Blades and McCabe had changed their stories. Webb also facilitated a meeting between the men and police investigators.

Sandeson only found out in the middle of his trial what Webb had done. His lawyers asked for a mistrial, and Webb was brought in to testify at a hearing without the jury in the courtroom.

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