The mother of a slain man cried Monday as the jury watched a video of a man on trial for first-degree murder describe killing her son in graphic detail.

Garry McGrath, 44, vanished in February 2004. His truck was discovered at the West Edmonton mall 12 days later.

George Allen, a 55-year-old truck shop owner, has pleaded not guilty to first-degree murder. His lawyer has argued Allen acted in self-defence.

Allen appeared to fight off tears as he watched the recording from the prisoner's box. McGrath's mother left the courtroom crying twice on Monday.

In the tape, Allen is talking to a man he thinks is with a criminal organization, but who is actually an undercover police officer secretly recording their conversation.

Allen tells the officer how tensions with McGrath escalated, in part over $24,000 he believed McGrath owed him but wouldn't pay.

Allen's wife confronted McGrath over the debt then McGrath complained about the confrontation to Allen.

"He'd a probably been OK if he had not come in there and called my old lady a bitch and my daughter a little slut. He'd a probably been OK," Allen tells the officer.

Disturbing details

In the videotape, Allen says McGrath pushed him.

Allen describes knocking McGrath down with a head-butt, and hitting him with a hammer when he tried to get up. Then, he says, he let McGrath bleed to death over a drain in a meat shop he has on his property.

"I just left him sitting there until he quit jibbering and shaking and then I went out and grabbed a big roll of … plastic. I come in, I laid it out, I rolled him up, taped it. Put the plastic this way, rolled him back. Taped it. Put it that way. I did that four times."

Investigators discovered McGrath's body on Oct. 14, 2005. It was wrapped in plastic and buried in a hole drilled on Allen's Antler Lake property east of Edmonton.

During the opening of the trial in late November, defence lawyer Kelly Dawson said much of Allen's statement to the undercover officers was a "total fabrication."

More of the videotape is expected to be shown when the trial resumes Tuesday.