Prosecutors charge that the Canadian captive, 21-year-old Omar Khadr, threw the grenade that fatally wounded Army Sgt. 1st Class Christopher Speer during a firefight at a suspected al Qaeda compound in Afghanistan. Khadr was 15 at the time.

Khadr's lawyer, Navy Lt. Cmdr. William Kuebler, said at a hearing on Friday that U.S. troops he questioned in preparation for trial had told him they threw grenades into the compound while other U.S. soldiers were inside.

"It's not beyond the realm of possibility that Sgt. Speer was killed by friendly fire," Kuebler said after the hearing at the controversial detention center for terrorism suspects set up at a U.S. naval base in Cuba.

"There were U.S. personnel employing hand grenades against combatants in the compound."

The possibility of friendly fire was the latest in a series of points raised by defense attorneys that cast some doubt, or at least clouded, the U.S. accusations against Khadr.

No one saw who threw the grenade and doctors who treated Speer at a military hospital in Germany did not save any of the shrapnel from his wounds, so there is no physical evidence that could have indicated the grenade's origin, Kuebler said.

Post-battle reports given to Khadr's lawyers did not mention the U.S. use of grenades during the battle, he said.

"There was an audible silence on the subject," said Kuebler, who has long argued that Khadr cannot get a fair trial in the U.S. war court at Guantanamo.

The chief prosecutor for the war court, Army Col. Lawrence Morris, dismissed the possibility of friendly fire.

"I am quite confident that that assertion will prove groundless when tested in court," he said, declining later to discuss the evidence outside the court.

The Bush administration considers the 280 Guantanamo prisoners to be unlawful enemy combatants undeserving of the legal protections granted to soldiers and civilians under international law. Rights groups have severely criticized the detention camp and the tribunals as a travesty of justice.

Kuebler has waged a publicity campaign in Canada in the hopes the Canadian government will repatriate Khadr for trial. Khadr's lawyer argues he was a child soldier forced into combat by his father, an alleged al Qaeda financier.

The prosecutor in the Khadr case, Marine Maj. Jeffrey Groharing, accused Kuebler of pursuing a political resolution of the case rather than preparing for trial, forcing delays that deprived Speer's widow and children of justice.

"There are real victims in this case and it is not the accused," he said. "Tabitha Speer is raising two children without her husband because of the acts of the accused."

The judge, Army Col. Peter Brownback, pointedly asked when Khadr was captured -- July 2002 -- and when he was first charged in the Guantanamo war court -- November 2005.

Those charges were thrown out when the U.S. Supreme Court struck down the first version of the Guantanamo court as illegal. They were refiled in April 2007 in the current version of the court.

Though Khadr is now a grown man with a full beard, the judge suggested that his age and treatment could be a factor leading to leniency in his sentence if he is convicted.

The judge ordered prosecutors to contact all the military commanders whose units were involved in Khadr's capture and detention and to find out what their policies were toward the treatment of juveniles.

"If they were violated that seems like a matter in extenuation," the judge said.

U.S. forces shot Khadr twice in the back in the firefight, interrogated him in Afghanistan as he recovered and then sent him to Guantanamo shortly after his 16th birthday. Khadr faces life in prison if convicted on all the charges against him.

(Reuters)