The U.S. Supreme Court on Monday rejected an appeal by a Canadian-born former Guantanamo detainee who was seeking to wipe away his war crimes convictions, including for killing a U.S. soldier in Afghanistan.

Omar Khadr had waived his right to appeal when he pleaded guilty in 2010 to charges that included murder. But his lawyers argued that a subsequent ruling by the federal appeals court in Washington called into question whether Khadr could have been charged with the crimes in the first place.

A divided three-judge panel ruled that, despite the appellate ruling, Khadr gave up his right to appeal.

Justices Brett Kavanaugh and Ketanji Brown Jackson did not take part in the Supreme Court's consideration of Khadr's appeal because both had dealt with the case while they served as appeals court judges. Jackson explained her recusal from Monday's order; Kavanaugh did not.

Khadr had been sentenced to eight years in prison plus the time he already had spent in custody, including several years at the U.S. naval base at Guantanamo Bay, Cuba. But he was released in May 2015 pending his appeal of the guilty plea.

A Canadian judge ruled in 2019 that his war crimes sentence had expired.

Khadr was 15 when he was captured by U.S. troops following a firefight at a suspected al-Qaida compound in Afghanistan that resulted in the death of an American special forces medic, U.S. Army Sgt. First Class Christopher Speer. Khadr, who was suspected of throwing the grenade that killed Speer, was taken to Guantanamo and ultimately charged with war crimes by a military commission.