Omar Khadr will be among a group of five terror suspects held in Guantanamo to be tried by military commission on U.S. soil.

By coincidence, the U.S. announcement on Friday came as the Supreme Court of Canada heard the federal government's argument for why it shouldn't be forced to bring Khadr home to be tried in Canada.

"We will as that case proceeds see how it should be ultimately treated," said U.S. Attorney General Eric Holder when asked about what would happen if the Canadian court ruled that Khadr should be repatriated.

Holder said five other suspects accused of plotting the 9/11 attacks, including self-professed mastermind Khalid Sheikh Mohammed will also be brought to the U.S. and tried in a New York City court. Holder said he will be seeking the death penalty for those five. He also said the group will be tried in civilian court because they are accused of attacking civilians.

He said those facing military commission are accused of military attacks.

Khadr, 23, is accused of throwing a grenade that killed a U.S. soldier during a firefight in Afghanistan in 2002. He is the only Canadian -- and is believed to be the only Westerner -- still being held at the U.S.-run detention centre on Cuban soil.

In a statement emailed to CTV News, Khadr's lawyer said he was disappointed in the decision he described as "devastating and shocking."

"We thought that the incoming Obama administration signaled a new day with respect to these cases, a new respect for civil liberties, an abhorrence of torture, a respect for the time-honored legal procedures and protections," Barry Coburn wrote.

Human rights group Amnesty International also criticized the U.S. ruling, arguing that Khadr should face the charges against him in a civilian court either in Canada or the U.S.

"The military-commission process is inherently flawed and simply can't deliver a fair trail," Alex Neve, secretary general of Amnesty International Canada, told CTV News Channel. "It completely lacks independence. That is, of course, the great benefit of going to the civilian court system."

Supreme Court hearing

In August, a Federal appeals court upheld a 2008 ruling that ordered Ottawa to take steps to bring Khadr, who was born in Toronto, home. It rejected the government's appeal because it said the government had "knowing participation" in his mistreatment in the Guantanamo Bay prison by sharing results of its interrogations with the Americans.

The decision was appealed and sent to the Supreme Court -- which was hearing arguments on the issue on Friday.

A federal lawyer in Ottawa argued in the Supreme Court that bringing Khadr home is a political choice to be made by a government, and not a decision to be made by a court of law.

"In my respectful submission, we're in the realm of diplomacy here," said Robert Frater.

He said the government had not ignored calls to bring Khadr back to Canada.

Nathan Whitling, Khadr's lawyer, argued that returning his client to Canada would help "lessen the harm" he has suffered.

Documents show Khadr has been threatened with rape, kept in isolation and intentionally deprived of sleep by his U.S. captors.

Chief Justice Beverley McLachlin said there's no doubt Khadr had "suffered greatly," but she wasn't sure whether bringing him to Canada would fix what's now in the past.

After Holder announced the decision, Canadian Intergovernmental Affairs Minister Pierre Poilievre told reporters in Ottawa that the government will continue to argue that it and not the court should decide whether to seek a Khadr trial in Canada.

"We believe the U.S. legal process announced today should run its course," Poilievre said.

He refused to clarify if his statement means the government would ignore a Supreme Court ruling order to seek Khadr's return from the U.S.

At least one constitutional law expert said that based on past experiences, the court is "somewhat sympathetic" to Khadr's situation.

"It's very hard at this stage to get a sense of where the court is going to go," said Cheryl Milne, who is Chair of the Ontario Bar Association's Constitutional, Civil Liberties and Human Rights section.

"They have in the past, very strongly found against the particular in relation to the interrogations," she told CTV News Channel.

Khadr has spent a third of his life in the Guantanamo Bay prison. He was sent there at age 15.

Khadr a 'child soldier'

Many have advocated on Khadr's behalf, calling him a child soldier who was raised by a family with ties to al Qaeda and Osama bin Laden. U.S. authorities allege he was recruited by his father, Ahmed Said Khadr who was an accused al Qaeda financier who was killed in Pakistan six years ago.

Ottawa has steadfastly refused to ask Washington to send him home to face the justice system here, saying it's not the government's place to meddle in another country's affairs.

Amnesty International has refuted the federal government's position, arguing that the Khadr case is about protecting the rights granted to Canadians under the Charter of Rights and Freedoms.

"This isn't a debate about whether or not the court is improperly intruding into foreign policy considerations," Neve said. "It's perfectly appropriate for the courts to step in when government does take action to contravene the Charter-protected rights of Canadians. That's what's at stake here."

Other Western countries such as Australia and the U.K. have successfully sought the repatriation of their citizens from Guantanamo, to face justice at home.

Khadr's U.S. military-appointed lawyer has maintained that Washington will allow his client to face prosecution on Canadian soil, if Ottawa puts forward the request.

U.S. court proceedings against Khadr began roughly four years ago and are before a military commission, but the hearings are on hold pending a review of his case.