(CNN) -- The youngest detainee at the Guantanamo Bay, Cuba, detention facility is to be tried next week by a military commission -- with a life sentence as one possible outcome -- and now his lawyer has gone to the U.S. Supreme Court to try to stop it.
Omar Khadr was 15 when he was apprehended in southeast Afghanistan in 2002, accused of lobbing a grenade that mortally wounded a U.S. medic. He also is accused of receiving one-on-one training from al Qaeda and being caught on a surveillance video making and planting roadside bombs where U.S. troops traveled.
Now 23, he faces trial at Guantanamo on August 10, on charges of murder and attempted murder in violation of the law of war, conspiracy, providing material support for terrorism and spying.
Khadr, a Canadian citizen who was born in Toronto, also is the only Westerner still held at the Guantanamo facility.
Initially, President Barack Obama's order to close the Guantanamo facility postponed the trial and left the case in limbo. But last November, his case drew the attention of Attorney General Eric Holder.
Holder made headlines that month by announcing that five detainees accused of complicitity in the September 11, 2001, attacks would be transferred to New York City to stand trial in a civilian court. At the same time, he clarified the status of Khadr and four others -- saying they would face military commissions.
The five due for trial in New York included the professed mastermind of the September 11 attacks, Khalid Sheikh Mohammed. Later, after local officials objected to the costs and potential security threats, the administration backtracked, putting the issue under review.
That leaves Mohammed in legal limbo for now, as Khadr faces trial in a matter of days.
But his military attorney, Army Lt. Col. Jon Jackson, has filed a petition with the U.S. Supreme Court to stop the military commission trial.
Jackson said in a statement accompanying the petition that "the sad truth is that military commissions are discriminatory" and provide "only second-class justice."
"If you are a citizen, like the Times Square bomber, you get all the protections of federal court. If you are a non-citizen, you are tried by military commission," he said. "This kind of discrimination is something we cannot stand for as a country."
He said that in previous wars, citizens and non-citizens received the same standard of justice.
"It didn't matter if you were German, British, Japanese or American. We stood for fairness and applied it," he said.
Jackson said he asked the Court of Appeals to hear Khadr's petition over four months ago. Now, he's asking the justices of the Supreme Court to either order the Court of Appeals to hear the case or decide it for themselves.
In an emergency motion, the Judge Advocate General's Corps lawyer is challenging the constitutionality of the Military Commission Act of 2009 and the validity of the proceedings against against Khadr.
Khadr was captured on July 27, 2002, after a Special Forces unit received intelligence that an al Qaeda explosive maker was in a mud-brick compound in Khost, a village near the Pakistani border, according to an affidavit by retired Special Forces Sgt. Layne Morris.
After soldiers formed a perimeter around the compound, two Afghan soldiers working with the Americans went to the gate and shouted in Pashto to surrender. The two were shot, point-blank, Morris said. The Americans returned fire and lobbed hand grenades.
They thought they had killed everyone, but what happened next is in dispute. Military prosecutors say that as soldiers walked into the compound, Khadr emerged from the ruins and threw the grenade that killed Sgt. 1st Class Christopher Speer. But the defense argues there was another man in the compound who could have thrown the grenade.
Speer, a 28-year-old father of two, was immediately taken from the scene by helicopter but died 10 days later.
Khadr, who was shot in the confrontation, was patched up and flown to Bagram Air Base in Afghanistan for questioning.
Khadr later claimed in a 2008 affidavit that his interrogators spat on him, pulled his hair and threatened him with rape at Bagram, although a defense attorney, Nathan Whitling, said the defense had no physical evidence to back up the account of torture.
It's also alleged in court documents that Khadr was part of a family that had an association with Osama bin Laden's training camps.
The documents say he was a toddler when his Palestinian mother and Egyptian father moved the family from Canada to Peshawar, Pakistan, to attend the al Qaeda camps.
The U.S. charges that the Khadr patriarch, Ahmed Khadr, later worked for charities in the Middle East and Canada that were fronts for al Qaeda. Omar Khadr's indictment says that in 1994, the father was arrested and served prison time for helping finance the bombing of the Egyptian embassy in Pakistan.
Omar Khadr and his siblings briefly returned to Canada during that time and then returned to Afghanistan, according to court filings.
The father later died in a gun battle with Pakistani police in 2003, according to Pakistani intelligence sources.