A Saudi prisoner who was being held at the Guantanamo Bay detention center has been released from U.S. custody, according to the Department of Defense in a statement issued Monday. Mohammad Ahmad al-Qahtani, who was previously accused of trying to join the Sept. 11, 2001, terrorist attackers, was sent back to Saudi Arabia from the U.S. military base in Cuba after a review board, including intelligence and military officials, concluded he can be safely released after spending about 20 years in federal custody. He will have to receive psychiatric treatment in his home country, the agency said. “The United States appreciates the willingness of Saudi Arabia and other partners to support ongoing U.S. efforts toward a deliberate and thorough process focused on responsibly reducing the detainee population and ultimately closing of the Guantanamo Bay facility,” the Department of Defense said. Medical examinations and records obtained by his attorneys suggest that al-Qahtani …