The five defendants were arraigned in May 2012 on charges that include terrorism and nearly 3,000 counts of murder in violation of the law of war for their alleged roles planning and aiding the attack on Sept. 11, 2001. They were transferred from CIA custody to Guantanamo in September 2006 and a previous effort to prosecute them by military commission was scuttled by an aborted attempt by the government to try them in civilian court.