The Supreme Court of Canada will hear arguments from Omar Khadr's lawyers about the legality of his detention and upcoming military trial at a U.S. naval base in Guantanamo Bay, Cuba. 

Omar Khadr, seen in 2002, is being tried for numerous charges, including murder, in a military trial at Guantanamo Bay military prison.
(Canadian Press)

In a ruling released Friday, the court dealt a blow to government lawyers and allowed Khadr's legal team to present fresh evidence it says demonstrates U.S. authorities are violating international law in their treatment of Khadr.

Khadr was captured in Afghanistan in 2002 when he was 15 and has since been held at the U.S. military base at Guantanamo Bay, Cuba.

He is facing numerous charges, including murder, in connection with the killing of a U.S. army sergeant with a grenade during a firefight between U.S. forces and Taliban fighters, in which the Toronto-born teenager was also seriously wounded.

The top court will be forced to examine whether the involvement and behaviour of Canadian officials were in conflict with Canadian domestic law, as well as Canada's obligations to international law and treaties, said Dennis Edney, Khadr's Canadian lawyer.

"We're gratified that the Supreme Court has decided that a full, complete record is before it in order to make a fair determination," Edney told CBCNews.ca in an interview Thursday from Edmonton.

Case goes before court next week

The court case stems from an earlier federal court decision that ordered the Canadian government to release documents to Khadr's lawyers for use in his defence against the murder charge. Ottawa appealed the ruling and arguments will be heard in the top court on March 26.  

But his lawyers also want to use the hearing to highlight the broader point that the Americans' handling of the case doesn't meet international standards of fairness.

"By being allowed to introduce fresh evidence, we will be showing that we have to talk about Guantanamo Bay," Edney said.

The federal Justice Department also filed a motion trying to quash that argument, saying a Canadian court is the wrong place to examine U.S. actions.

Among the issues expected to be raised before the court are Khadr's age at the time of his capture and the contradictory evidence emerging from U.S. authorities in recent weeks from his pre-trial hearing at Guantanamo.

Khadr deserves child soldier status: U.S. military lawyer

Khadr's U.S. military defence lawyer has repeatedly dismissed the military tribunals as illegal and unfair, and has also questioned whether Canada has done enough to advocate on Khadr's behalf to their American counterparts.

Lt.-Cmdr. Bill Kuebler has stated Khadr is clearly a child soldier and, under international obligations, should be released and helped to reintegrate into society.

The United States and Canada are signatories to a United Nations protocol that states fighters under age 18 are to be considered child soldiers.

In an affidavit released Tuesday, Khadr alleges U.S. military interrogators in Afghanistan threatened him with rape and treated him harshly, forcing him to make false and self-incriminating statements.

He also claims Canadian diplomats and intelligence officers who questioned him at Guantanamo refused to help, accused him of lying, and passed information from their interviews to U.S. officials.

Meanwhile, documents released by the Pentagon on Thursday include an account of the 2002 gun battle by a U.S. army officer who admits he nearly ordered Khadr's execution. The officer also confirms an earlier account that Khadr was not the only Taliban fighter alive when the grenade was thrown.

With files from the Canadian Press