A never-before-disclosed American eyewitness to the furious battle in Afghanistan where Omar Khadr allegedly tossed a grenade has cast doubt on whether the teenager was an “unlawful” combatant, his defense team said this week.

Britain’s Prince Harry sits on his camp bed at FOB Delhi, in Helmand province, southern Afghanistan

The stunning disclosure, after a short and largely uneventful arraignment Thursday, was the latest twist in the tortuous process of bringing the only Canadian held at Guantanamo to trial.

It remains unclear whether Thursday’s revelation amounts to a bombshell that shatters the government’s case – conceivably by showing that Mr. Khadr has Geneva Conventions protection as a legitimate combatant, and thus throwing a grenade was combat, not murder – or just adds new complexity and further delay to the case.

Mr. Khadr, now 21, attended Thursday’s proceedings and quietly accepted his assigned U.S. military lawyers, calmly answered questions from the judge and seemed attentively engaged by the process. He exercised his right to defer entering a plea to the charges.

But defense lawyers suggested the eyewitness account could undermine the central prosecution claim that Mr. Khadr was an “unlawful” enemy combatant and thus can be tried as a war criminal for killing a U.S. Special Forces medic.

Because the eyewitness’s identity remains a secret and his account is classified, defense lawyers couldn’t provide, and don’t know, all the details. It came from a “U.S. government employee,” confirmed Lieutenant-Commander Bill Kuebler, the U.S. navy lawyer heading Mr. Khadr’s defense.

That wording suggests, perhaps, a Central Intelligence Agency operative, some of whom are known to have been with U.S. Special Forces in Afghanistan.

In July of 2002, a U.S. Special Forces group fought a gun battle at a remote compound near Khost in eastern Afghanistan. The only survivor among those engaged by the U.S. forces was the teenaged Mr. Khadr, then 15, who was gravely wounded. An American medic was killed in a grenade explosion and several other U.S. soldiers were injured.”

It’s classified evidence of an exculpatory nature,” Lt.-Cmdr. Kuebler said, adding prosecutors “made us aware of this at the last minute.” Some observers, flown to Guantanamo to witness the proceedings, denounced the prosecution.

“It is totally outrageous that the prosecution would try to push ahead with a hearing on whether or not Khadr was an unlawful enemy combatant, while all the time withholding from the defense potentially exculpatory information,” said Jennifer Daskal of Human Rights Watch. “Anyone who has ever gone to law school knows the fundamental legal and ethical rule: The prosecution cannot withhold exculpatory information from the defense.”

Others, like James Carafano of the Heritage Foundation, a conservative think tank, praised the open, adversarial character of the proceedings. “Today the American people had a good day, today the system won,” he said.

Nevertheless, not only might the eyewitness evidence have a significant bearing on the case, defense lawyers were at pains to claim that the secrecy and pattern of lack of disclosure underscore the problems inherent in the process.

Several prosecution witnesses, including a Federal Bureau of Investigation interrogator, have flatly refused to even be interviewed by defense lawyers, Lt.-Cmdr. Kuebler said.

“How much more exculpatory evidence is out there, somewhere?” he asked at a news conference after the hearing.

Disclosure of the eyewitness’s existence didn’t occur during the two-hour hearing, when, it seems, Mr. Khadr’s long-delayed trial finally got under way more than five years after he was brought to this special prison for terrorist suspects at the U.S. naval base in Cuba. Instead, it was first revealed to the press by Michael Berrigan, the deputy chief defense counsel, who suggested questions be put to prosecutors as to why it had not been disclosed to the defense until 36 hours before the court appearance.

The prosecution team declined to provide any explanation or meet with the news media group flown in to Guantanamo for the hearing.

“They are going to do their talking in the courtroom,” said Lieutenant-Colonel Rick Helmer, who said he was authorized to deliver a message from prosecutors.

But it may explain why Army Colonel Peter Brownback, the presiding military judge, flatly refused to let prosecutors proceed with their effort to portray Mr. Khadr as an al-Qaeda member. Their effort to play a video purportedly showing Mr. Khadr making roadside bombs was bluntly rejected by the judge, who had been told at a meeting prior to the hearing about the mystery eyewitness.

Marine Major Jeffrey Groharing said he could show Mr. Khadr was an unlawful combatant if allowed to present the video purportedly recovered from the compound where the battle occurred.

During the hearing, Col. Brownback rejected a defense challenge that he was unfit to preside and ordered both sides to get pretrial motions ready by next month.

In striking contrast to his previous appearances before the military tribunal, Mr. Khadr was attentive and relaxed during the session. Full-bearded, wearing freshly laundered and strikingly white baggy pants and long, loose overshirt, the attire assigned prisoners considered the most compliant with the rules, with his long hair neatly coiled inside a black stocking cap, Mr. Khadr was marched into the court by two towering soldiers.

Once seated, he ignored the “All rise” as Col. Brownback strode into the converted courtroom inside an old airport terminal building. But Mr. Khadr did stand when instructed by the military judge, who asked him if he accepted his assigned military counsel. “Yes sir,” he said clearly when the judge asked whether he could hear him. And then, without hesitation, Mr. Khadr politely replied “Yes” to a short series of questions about whether he was satisfied with his defense team that now includes two Canadian lawyers who have only advisory status in the court.

Otherwise he sat, engaged, playing occasionally with papers on the polished table before him or tapping his thumbs silently as the teams of lawyers thrashed through a procedural session.

After a quick lunch with his lawyers, during which Mr. Khadr apologized for not having food for everyone, he disappeared back to the complex of prison camps along the Cuban coast. He isn’t expected back in court until some time next spring, although no trial date has been set.”

He’s a decent young man with a good heart, suffering from a terrible injustice,” Lt.-Cmdr. Kuebler said. Mr. Khadr’s lawyers are preparing a two-pronged defense: attempting to undermine the prosecution’s case while challenging the legality of the entire military-commission process.

“This is a process that was not designed to be fair,” Lt.-Cmdr. Kuebler said. “We don’t expect a fair trial for Omar Khadr. … Our ultimate hope is that Canada, like Britain and Australia,” will demand the repatriation of its citizen.

Mr. Khadr, whose father was a friend of al-Qaeda leader Osama bin Laden, is charged with murder, attempted murder, conspiring with al-Qaeda, providing material support for terrorism and spying by conducting surveillance of U.S. military convoys in Afghanistan. He faces life in prison if convicted. If he is acquitted, senior Bush administration officials have said he might remain detained indefinitely at Guantanamo anyway.

The Toronto Globe and Mail