| The case of a mentally ill detainee at Guantánamo Bay, Mohammed al-Qahtani, has long confounded the United States government. Suspected of being Al Qaeda's intended 20th hijacker in the Sept. 11, 2001, attacks, he was tortured by military interrogators early in his detention at the American naval base in Cuba. A senior Pentagon official later determined that, because of how Mr. Qahtani was initially treated, he could not be prosecuted. Security officials also considered him too dangerous to release, so he has remained detained for two decades. | 
