Lawyers for the widow of a U.S. soldier slain in Afghanistan have filed court papers in Canada formally seeking to take millions of dollars away from a former Guantanamo Bay prisoner who pleaded guilty to killing the soldier.

Omar Khadr was reportedly paid 10.5 million Canadian dollars ($8 million) by Canada's government last week under a court ruling that his rights were violated by Canadian officials while he was locked up at the U.S. military base on Cuba.

The Canadian-born Khadr was 15 when he was captured by U.S. troops after a firefight at a suspected al-Qaida compound in Afghanistan that resulted in the death of U.S. Army Sgt. First Class Christopher Speer. Khadr was suspected of throwing the grenade that killed Speer.

Tabitha Speer, the soldier's widow, and former soldier Layne Morris, who was blinded in the 2002 firefight, won a wrongful death judgment of $134.1 million against Khadr two years ago in Utah.

Lawyers for the pair filed a motion in the Ontario Superior Court of Justice this week asking that the judgment be enforced in Canada and that Khadr's assets be frozen until payment of the Utah judgment is sorted out.

Khadr's lawyer, Nate Whitling, said Wednesday that Speer's lawyers did not offer substantial evidence to support the plea.

"The scant evidence offered in support of this pleading consists of double and triple hearsay statements drawn from media reports and Wikipedia," Whitling wrote in a court filing urging the court to dismiss the families' request against Khadr. "The hearsay now relied upon by the applicants is so vague and unreliable as to be of zero probative value."

Whitling said Speer has failed to show there is a real risk Khadr is hiding his money as a way to avoid paying people he might owe.