Attorneys for a Canadian man who spent a decade detained by the United States military at Guantanamo Bay say details in the Obama administration’s recently released “drone memo” exonerates their client of war crimes.

Omar Khadr was only 15 years old when he was captured by American forces in Afghanistan in 2002 and taken to the Bagram Air Base, then Guantanamo, where he later pleaded guilty to murder in violation of the laws of war — according to military prosecutors, Khadr tossed a grenade that killed Sgt. Christopher Speer.

After being transferred to Canadian custody in 2012, Khadr said he pleaded guilty to war crimes because he was "left with a hopeless choice" of either accepting the charges or risk facing "continued abuse and torture" at the hands of his Gitmo jailers.

But in a recent court filing [PDF], lawyers for Khadr, now 27, say a just-published US Department of Justice memorandum contains information that directly challenges the American government’s case against their client.

Khadr’s attorneys wrote this week that the secret “drone memo” released by the White House last month — the DOJ document that the government relied on to justify the 2010 drone strike in Yemen that killed American citizen and suspected AL-Qaeda member Anwar Al-Awlaki — suggests prosecutors had no place to charge the Canadian teenager with murder in violation of the laws of war after he allegedly killed an American soldier during a firefight in Afghanistan.

The DOJ memo itself was a penned by the department’s Office of Legal Counsel in response to the question of whether Central Intelligence Agency officers — who are not members of the US military — can be blamed for war crimes by launching drone strikes. The memo was written in July 2010, and justified the strike that later that year killed Al-Awlaki.

According to a footnote within the memo, released June 24 of this year due to a Freedom of Information Act lawsuit, “lethal activities conducted in accordance with the laws of war, and undertaken in the course of lawfully authorized hostilities, do not violate the laws of war by virtue of the fact that they are carried out in part by government actors who are not entitled to the combatant’s privilege.”

"That completely blows away one of the major prongs of the government's theory in all these Guantanamo cases," Sam Morison, Khadr's Pentagon-based lawyer, told The Canadian Press during an interview on Wednesday this week.

Although Khadr was charged with violating the “US common law of war” that dates back centuries, his attorneys say the memo concerning CIA drone strikes suggest such legislation simply doesn’t exist.

"The whole purpose...was to evaluate whether the CIA agents were violating the law," Morison said. "The only reasonable interpretation of that analysis is that there is no such thing (as the common law of war)."

On Monday this week, Morrison and the rest of Khadr’s legal counsel, filed a motion in Guantanamo’s appeals court asking that the conviction against their client be vacated.

“The Americans made up serious charges that they knew were false,” Dennis Edney, a Canadian based lawyer for Khadr, told the Toronto Star this week. “It’s a complete violation of everything we understand about justice.”

Should Khadr’s attorneys succeed, then a number of cases pertaining to current or former Guantanamo detainees accused of war crimes could be called into question. According to Human Rights Watch, however, only six of the 149 detainees at Gitmo face any formal charges — fewer than the number of prisoners who have died while held there in military custody.