Defence lawyers for Canadian terror suspect Omar Khadr are investigating whether a video released to the media may have been leaked by the office of U.S. Vice-President Dick Cheney.

The video, broadcast last November on 60 Minutes, appears to show Khadr building a roadside bomb in Afghanistan.

Lt.-Cmdr. William Kuebler said his recent court filing cites Col. Morris Davis, the former chief proscutor of the military commission that will be trying Khadr in Guantanamo Bay, as stating that he believes the video came from Cheney's office.

That opinion was based on conversations Davis had with 60 Minutes producers, Kuebler said. The producers of the show have refused to officially reveal how the video was obtained.

"Based on his claim or his belief, we're going to conduct an inquiry into whether or not that's true," Kuebler told CTV's Canada AM.

"There's really nobody closer to the process over the last couple of years to the process than Col. Davis. He thinks it's possible or likely this tape came from the vice-president's office, so that's very significant."

If the defence can prove that the video was in fact leaked by someone in Cheney's office, it would represent a "clear violation of the protective orders that are in place," he said.

"They prohibit me from discussing just about anything included in the government's case against my client, so if the government isn't abiding by its own rules, I think that's a clear violation of those orders," Kuebler said.

Davis resigned from his post as chief prosecutor last October, claiming political interference was keeping him from doing his job properly.

Omar Khadr faces a trial on charges that include murder, related to a 2002 firefight in Afghanistan that left a U.S. soldier dead.

Kuebler said the military prosecutors "desperately" wanted to play the video before the media last November when the case was before the court in Guantanamo Bay.

"They didn't get the chance to do it, and low and behold it ends up on 60 Minutes a couple of weeks later," he said, adding that prosecutors have considered the video the "smoking gun" in their case against Khadr.

However, Kuebler dismissed the importance of the leaked footage.

"I think the tape, at worst, if in fact it is what the government says it is, shows that Omar Khadr was exploited and used as a child soldier by much older people in Afghanistan, which is what we've always said," Kuebler said.

Khadr's trial is expected to begin later this year. He could face a possible life sentence if convicted.