He was the first child soldier to be prosecuted by a Western country since World War II, dragged out from under the rubble of a Jihadist compound bombed by the US in the state you can see above. He was a 15-year old Canadian who was interrogated thus:
During pretrial hearings, Khadr's lead interrogator at Bagram admitted in court that, in addition to yelling, cursing and throwing furniture during interrogations, he had told Khadr a fictitious story about another Afghan teenager captured by U.S. forces who was gang-raped by "big black guys" in prison and likely killed by them, all because he didn't cooperate with interrogators. This "Interrogator #1" -- who was later court-martialled for abusing other prisoners -- interviewed Omar Khadr about 25 times. Khadr's lawyers made a motion to suppress Khadr's statements on the grounds that they were elicited by torture and abuse.
Khadr himself has claimed via Wiki:
that he was refused pain medication for his wounds, that he had his hands tied above a door frame for hours, had cold water thrown on him, had a bag placed over his head and was threatened with military dogs, was flatulated upon, forced to carry 5-gallon pails of water to aggravate his shoulder wound. Unallowed to use washrooms, he was forced to urinate on himself. His chief interrogator was Joshua Claus, who later pleaded guilty to abusing detainees to extract confessions following the in-custody death of wrongly accused Dilawar that same year.
Confessions made under those circumstances were allowed in his trial. He has subsequently confessed to more crimes than he had originally been charged with. It seems he was indeed involved in a firefight in Afghanistan which became very deadly, had been caught up with Jihadists connected with his father, and had prepped explosives. He was not innocent of involvement with al Qaeda; but he was 15 years old, and in the battle that wounded him (whose complicated and contested details you can read about here) he was in a compound blasted with 500 pound bombs, buried under rubble, shot twice in the back, and sustained injuries that left one eye blind and the other with shrapnel still embedded. This is what remained of the building he was in after the bombing, of which he was the lone survivor:
If Khadr had gone to trial, he faced a potential life sentence from a military jury, who would hear how he "confessed" to the crimes in interrogation. He could have faced many more years in prison. What's more, the U.S. maintains the right to indefinitely detain him even if he was found not guilty.
His plea allows him to be released to a Canadian jail to serve out seven of his eight remaining years. Somehow, I doubt he will remain behind bars once he is remanded to a country that obeys international law about treatment of child soldiers and prohibits abuse, coercion and torture in interrogations. But it remains a source of shame for Canada's government that, for so long, it bowed to US pressure and did so little to rescue this misguided teen from the custody he will now have to endure for only one more year.
I don't know how anyone who cares about the integrity and moral standing of the United States can absorb the full details of this case and not be profoundly ashamed. To prosecute a child soldier, already nearly killed in battle, tortured and abused in custody, and to imprison him for this length of time and even now, convict him of charges for which there is next to no proof but his own coerced confessions ... well, words fail.