The 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.