GUANTANAMO BAY, Cuba - Canadian war-criminal Omar Khadr deserves to serve 40 more years behind bars for war crimes, a military jury decided on Sunday, but their decision was overruled by a pre-trial agreement that capped his sentence at eight years.

After more than eight hours of deliberations over two days, the seven military officers called for the hefty punishment not knowing about the agree-on cap.

The pre-trial agreement also calls for Khadr, 24, to serve one more more year in U.S. custody, where he has been for the past eight years. The U.S. government would support his bid to apply to serve the rest of his sentence in a Canadian prison.

A spokeswoman for Foreign Affairs Minister Lawrence Cannon would not speculate on whether Canada would agree to the request.

"Should Omar Khadr submit an application, he would be treated like any other Canadian who applies for a transfer," Melissa Lantsman said in an email. "The decision on any potential transfer will be made in accordance with current law. No decision can be made until an application is received."

Khadr's Canadian defence lawyer Dennis Edney denounced the process that saw the first juvenile prosecuted for war crimes in six decades.

"The fact that the trial of a child soldier, Omar Khadr, has ended with a guilty plea in exchange for his eventual release to Canada does not change the fact that fundamental principles of law and due process were long since abandoned in Omar’s case," Edney said.

"In exchange for repatriation, Omar was required to sign an admission of facts which was stunning in its false portrayal of him."

The jury sentence was much stiffer than the 25 years the prosecution had wanted.

After they announced their sentence, presiding judge Col. Patrick Parrish thanked the officers, dismissed them, and imposed the eight-year sentence agreed to before trial.

Before announcing its decision, the panel asked the judge to replay the testimony of a defence witness who spoke of Khadr's "rehabilitative" potential.

The panel deliberated longer than any other military-commission sentencing jury. Under the rules, at least six of the seven jurors had to agree on the punishment they wanted.

The prosecution on Saturday called for at least 25 years on top of the eight Khadr has spent in custody since being captured as a badly wounded 15 year old in the rubble of a bombed-out Afghan compound in July 2002.

"Make no mistake. The world is watching," prosecutor Jeff Groharing told the panel Saturday morning. "Your sentence will send a message."

However, the defence stressed Khadr's age when he committed his crimes, including the murder in violation of the laws of war for the killing of Sgt. 1st Class Chris Speer in the July 2002 firefight.

More than 1,000 American service members have been killed in Afghanistan but Khadr is the only captive the U.S. has charged with murder in connection with a death. Khadr himself gave a statement to the sentencing hearing, saying he was "really, really sorry" for the pain he had caused Speer's wife and children.