A polygraph test was the catalyst as Niagara Regional Police investigator Paul Granton spent hours trying to coax a confession out of Mike McNeil.

After unhooking McNeil from the machine, Granton pulled his chair close and looked McNeil in the eye.

"There is no doubt in my mind that you were involved in (the victim's) death," Granton said.

"You're wrong," McNeil snapped back.

McNeil, the victim's boyfriend, is giving his evidence in Michael Durant's first-degree murder trial via video recordings of statements he made to police.

McNeil died in 2004, one year after his girlfriend was murdered, and eight years before Durant first went to trial.

A jury convicted Durant in fall 2012, but the Ontario Court of Appeal overturned the verdict.

The polygraph was floated to McNeil by homicide investigator Mike Matthews. Matthews told McNeil the results would clear him in his girlfriend's death, and allow the police to focus on finding the real killer.

Granton, a trained polygraph administrator, tested McNeil three times in August 2003, with the last taking place Aug. 18, nine days after a passerby spotted a body in a ditch off Darby Road on the outskirts of Niagara Falls near the border with Welland and alerted police.

"I know you have a moral background," Granton said to McNeil. "I want to know what happened to make you act so out of character. I want to know why."

McNeil had told the investigators he and his girlfriend were heroin addicts, and she was working the street for money to buy drugs.

"Drugs are a driving force in your life," Granton said. "You didn't want her out there working the streets, but she went anyway. You didn't like the skimpy clothes she was wearing.

"You wanted the best for her, and your level of frustration grew."

Said McNeil: "You're fishing here. You are going on about how caring I am. How could you think I did this?"

Granton administered the first polygraph just days after the victim's body was discovered.

Polygraph devices measure changes in the subject's blood pressure, pulse, respiration and skin conductivity in response to questions.

The evidence isn't admissible in court, but any remarks - or confessions - made by the subject during the test are.

Earlier in the trial, Durant was overheard on a wiretapped conversation with his former wife, Dana Arnold, blaming the murder on McNeil and another man.

Defence attorney Joe Wilkinson has told Justice Gerald Taylor he intends to use an alternative suspect theory in Durant's defence.

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Wilkinson is scheduled to bring his evidence in May, after a break in the trial and the Crown wraps up its case.

Durant, 45, of Niagara Falls, is on trial in the killing of a woman in 2003.

The victim's name, as well as any information that might identify her, is protected by a publication ban. The trial is being held in Kitchener.