Former Guantanamo Bay prisoner Omar Khadr cannot avoid a huge civil judgment against him by recanting the confession and guilty plea he made before an American military commission, lawyers acting for the widow of a U.S. special forces soldier argue in new court filings.

Canadian courts must accept the agreed statement of facts that underpinned Khadr's war-crimes conviction in 2010, they argue, regardless of whether he lied under oath when he admitted to tossing a hand grenade that killed the soldier eight years earlier.

"No court anywhere, either in Canada or the U.S., has found the (agreed statement) specifically was involuntary or the product of coercion," the lawyers state in their filing last month. "A sworn confession is not lightly ignored, particularly when (Khadr) benefited significantly from it in terms of a plea agreement resulting in a reduced sentence and the eligibility to be commuted back to Canada."

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Nor is it relevant, they argue, how Khadr was treated after American forces captured him as a 15-year-old in Afghanistan in July 2002 and shipped him off to the infamous prison where, Canadian courts have concluded, he was abused and his rights violated.

The lawyers are calling on Alberta's Court of Queen's Bench to enforce a US$134-million judgment against Khadr handed down in Utah in June 2015 in favour of Sgt. Chris Speer's widow, Tabitha Speer, and former U.S. special forces soldier Layne Morris. Chris Speer was killed following a massive U.S. assault on an insurgent compound in which Khadr was badly wounded. Morris was blinded in one eye during the same operation.

In exchange for a further eight-year prison term and the promise he could serve most of it in Canada, the Toronto-born Khadr admitted in 2010 before a widely discredited military commission in Guantanamo Bay to having thrown the grenades that killed Speer and injured Morris.

Khadr later said that his detailed confession – contained in a lengthy agreed statement of facts written by American military prosecutors – and guilty plea to five purported war crimes were his only way to be returned to Canada. He also now says he doesn't remember what happened during the four-hour Afghanistan assault.

In defending against the enforcement application in Alberta, Khadr maintained he was a child soldier whose rights were violated by both his American captors and Canadian officials. His Edmonton-based lawyer, Nate Whitling, asserted in a statement of defence filed in November that the military commission was a bogus court that prosecuted made-up crimes without regard to Khadr's age and complaints of torture.

The Supreme Court of Canada, Whitling notes, found that Khadr made self-incriminating statements to American and Canadian officials at Guantanamo while detained under conditions that "offend the most basic Canadian standards about the treatment of detained youth suspects."

The federal government apologized to Khadr and, in a move still having political repercussions, paid him $10.5-million last summer to settle a civil claim he made against Ottawa. Word of the settlement prompted the American plaintiffs to make an unsuccessful bid to have an Ontario court freeze his assets while they fought to enforce the Utah judgment in Canada.

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Given the Supreme Court findings and Ottawa's apology to Khadr, Whitling maintains that recognizing the Utah award would "offend Canada's public policy principles."

In rebuttal, the Americans' Calgary-based lawyer Dan Gilborn argues Canada, like Utah, has legislation that allows victims of terrorism to sue for damages.

"There can be no breach of Canadian public policy to enforce a judgment obtained in the same way a Canadian can obtain a similar judgment," says Gilborn, who argues Khadr didn't qualify as a "child soldier."

Nor is it the role of a Canadian court to effectively act as an Appeal Court for the American military commission proceedings, Gilborn says.

To avoid running afoul of procedural time limits, Gilborn said the Alberta case might yet be put on hold in favour of a similar application in Ontario. That action, filed last June, has seen little movement beyond an initial flurry of activity. Whitling had no comment on any potential agreement to set the Alberta proceedings aside.

Khadr, 31, who is now married, was released on bail in Alberta in 2015 pending the outcome of his stalled appeal in the U.S. of his military commission conviction.

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None of the Americans' arguments nor Khadr's defence against them related to the Utah judgment has been tested in a Canadian court.