|Khadr, right, has pleaded guilty to five charges as part of a plea bargain [Reuters]
A Canadian-born detainee on trial at the US military prison at Guatanamo Bay has apologised to the widow of a US soldier he killed in Afghanistan.
"I'm really sorry for the pain I caused to your family. I wish I could do something to take that pain away," Omar Khadr said on Thursday in his first remarks to the military tribunal.
Tabitha Speer had earlier spoken at the trial about her husband, a special forces medic who was mortally wounded by a grenade that Khadr admits throwing during a four-hour battle.
"My husband was a good man," she said. "You will forever be a murderer in my eyes."
Speer said that Khadr, who was aged 15 at the time of his capture, must be held responsible for his actions despite his youth as he had chosen to remain at the compound when US forces had allowed women and children to leave.
"You had your choice and you stayed," she said during an hour of testimony.
"Everyone wants to say he's the child, he's the victim," Speer said. "I don't see that. My children are the victims."
She also read from letters written by daughter Taryn, 11, and eight-year-old son Tanner. Taryn, addressing her words directly to Khadr, wrote how she was mad "at you for what you did to my family. Because of you, my dad never got to see me play soccer... you make me really sad".
Khadr bowed his head as Speer spoke and did not look up as she directly addressed him.
Khadr admitted to the killing of Army Sergeant 1st Class Christopher Speer as part of a plea deal that was announced to the court on Monday. He also admitted placing 10 roadside bombs in Afghanistan and spying on US convoys to assess the best ways to attack them.
The exact terms of the plea deal were not immediately disclosed, but Khadr is due to be sentenced by a military jury in the coming days. The sentence they impose is bound by the plea deal.
Khadr would be allowed to trasfer back to his native Canada after serving a year of his sentence as part of the deal, the military judge in charge of the case said.
The seven-member military jury is hearing testimony to recommend a sentence against Khadr which will only have force if it is less severe than under the plea deal terms.
The UN representative for children and armed conflict has urged the military tribunal to release Khadr and send him to a rehabilitation programme in Canada, comparing him to other youths who have been recruited to fight by unscrupulous adults.
"In every sense Omar represents the classic child soldier narrative," Radhika Coomaraswamy, a UN undersecretary-general, wrote in a letter.
Also on Thursday, a US Navy captain who worked at Guantanamo told the hearing that Khadr showed strong potential for turning his life around and that he had not seemed radicalised like other detainees.
"I believe that his age, his lack of experience, the fact that his father took him to Afghanistan leads me to believe he has rehabilitative potential," Captain Patrick McCarthy, a witness for the defence, said.
He said other detainees were "fanatical" but Khadr was different. "He was always very respectful," he said.