TORONTO - A new documentary promises to uncover the truth about the murder of Jennifer Jenkins, a Chatham, Ont., native whose brother was convicted of her killing.

"Life With Murder," airing Tuesday on CTV, features extensive interviews with Mason Jenkins, who's serving a life sentence for first-degree murder, and with his parents, who remained devoted to their son as the grisly case unravelled.

For years, Mason Jenkins insisted he was innocent. And award-winning director John Kastner says his film unearths information that will be shocking even to people who followed the case closely.

"To our amazement, we were able to establish who really killed Jennifer Jenkins," Kastner said in an interview from his tree-shaded Toronto home. "The killer confesses on camera. And one of the amazing things about the film is that the parents are finding out all these things for the first time.

"They're finding out for the first time who really killed Jennifer, they're finding out what happened that night and why it happened, so it was a completely unexpected series of revelations. Going in, we certainly had no idea that all this stuff was going to come out.

"It's quite unique. It's quite amazing."

If it sounds as though Kastner is being a bit coy with the details, that's because he considers his documentary a "real-life murder mystery."

Indeed, "Life With Murder" unspools at a careful, deliberate pace, with new details being guarded closely until their reveal yields maximum impact on the viewer.

Kastner's interest in the personal relationships of criminals dates back to his youth.

When he was 16, Kastner was cast as an actor in a training film for prison guards shot at Collins Bay penitentiary in Kingston, Ont. He found himself spending his free time during the shoot chatting with incarcerated criminals, and became fascinated with the disconnect between the terrible deeds committed by some of the inmates and their otherwise normal demeanours.

And the three-time Emmy winner remains interested in that relationship.

"I've been doing this for almost 30 years, I've been in and out of so many prisons, it's like a second home to me," he said with a sly smile.

"It's like 'Apocalypse Now' -- 'I love the smell of napalm in the morning.' Well, I love the sound of keys turning in locks, I guess."@

Kastner first heard about the Jenkins while producing "Monster in the Family," about Martin Ferrier.

In 1998, 18-year-old Jennifer Jenkins was shot five times and killed. Her older brother, Mason Jenkins, was the primary suspect and was eventually convicted of first-degree murder.

He insisted he didn't do it and his parents supported them, even as details of the case gradually emerged.

At first, the story didn't really capture Kastner's interest as a filmmaker.

"Then I heard rumblings through the grapevine that Mason was beginning to disclose that he knew a little bit more about what had happened that night," Kastner recalled. "So I began to talk to him."

That was 2005. Kastner didn't begin work on the film until the spring of 2008, when he and Jenkins had already formed a bond.

By gaining the trust of Jenkins and his parents, Kastner earned unprecedented access. He managed to wrangle police video of the Jenkins family being interrogated following the murder and even sat in on Brian and Leslie Jenkins' visits to their son, moments so personal and fraught with emotion it's hard to believe the family consented to their filming.

"One of the amazing things about the Jenkins is that they never talked about the murder to Mason," Kastner said. "Initially, because they were witnesses at the trial and it's not permitted, but after several years, they just got into the habit of not discussing it.

"And frankly, I think that part of it was a coping mechanism for them. They parked all of this in a drawer. ... How much pain can a human being stand, basically?"

Kastner said the couple was vindicated by the rapturous reception his film received when it aired at Toronto's Hot Docs festival earlier this year (the doc also did the rounds at the Los Angeles Film Festival).

Attending the film's spring premiere, Brian and Leslie Jenkins received a standing ovation after the film that Kastner said "thrilled" the couple.

He says Mason Jenkins is nervous about the impending broadcast premiere of the film, and the potential reaction of his fellow inmates.

"I think he's relieved to find that he thinks we did a fairly balanced job of it," Kastner said. "But it's nerve-wracking to be exposed like that on national television in such a major way, and you have no control whatsoever of it."

Kastner has kept in touch with Jenkins since he completed work on the film. Which begs the question, why stay on friendly terms with someone convicted of murder?

"All I can say is that I've dealt with worse offenders than Mason," Kastner replied.