Former Guantanamo Bay prisoner Omar Khadr tries again Wednesday to expand his civil lawsuit against the federal government to include a claim that Canada conspired with the United States for what he says was the abuse of his rights and torture.

The proposed $20-million action foundered last December when Federal Court Judge Richard Mosley ruled the amended lawsuit, initially filed in 2004, needed to be rewritten before it could proceed on its merits.

A key issue is whether Mosley will now allow Khadr to press his conspiracy claim — a cause of action the federal government says should not be available to him.

In essence, Khadr wants to argue that Canada conspired with the U.S. in breaching his charter rights when intelligence agents went down to Guantanamo Bay to interview him in 2003 and 2004. The conspiracy claim — if successful — would tie Canada's conduct to that of the United States.

"A conspiratorial claim (would make) Canada liable for the torture that was committed by the States," Khadr's lawyer, John Phillips, said in an interview Tuesday.

"I want Canada liable for the torture."

U.S. gave Canada conditional access to Khadr

None of the allegations has been proven in court. The U.S. government has denied Khadr was seriously abused or tortured.

Documents show the RCMP was building a terrorism-related case against the Toronto-born Khadr at a time the Americans were developing war-crimes charges against him.

American authorities allowed Canadian agents access to him at the Guantanamo prison only if they shared any intelligence they gained, which they did, the documents show. Khadr was never told he was the target of a criminal probe in Canada or about the information-sharing deal.

Following that agreement, Khadr's military captors subjected him among other things to sleep-deprivation — known as the "frequent flyer" program — to soften him up for interrogation by Canadian authorities, something Mosley acknowledged when he refused to shut the door to the conspiracy claim.

Mosley also noted that Federal Court would not have to pass judgment on the legality of what the U.S. did to Khadr, but on whether Canada's agreement with the Americans to share information to be used in prosecuting him was legal.

If Mosley rules the conspiracy claim can proceed, Khadr's lawyers say it would likely pave the way for the production of documents that could help him in his suit and in his quest for damages.

Khadr faces $45-million US lawsuit

Khadr, who turns 28 later this month, was 15 years old when the Americans arrested him in July 2002 following a brutal firefight in which he was horrifically injured and an American special forces soldier was killed.

He ultimately pleaded guilty to five war crimes — including murder in violation of the law of war — before a widely maligned military commission in October 2010 and was sentenced to a further eight years.

He transferred to Canadian custody in September 2012 and later said his guilty plea was a desperate act to get out of American custody. He is currently incarcerated in the Bowden Institution in Innisfail, Alta. Ottawa insists he's an unrepentant, hardened terrorist.

Meanwhile, Khadr has yet to find an American lawyer willing to defend him against a $45-million US lawsuit filed in Utah in May by the widow of the U.S. special forces soldier killed in Afghanistan and another American soldier blinded by a grenade. That leaves open the possibility of a default judgment against him.

It remains far from clear, however, whether Canadian courts would enforce any such judgment.