The alleged "20th hijacker" in the Sept. 11 attacks tried to kill himself at Guantanamo last month, his lawyer disclosed Tuesday, saying the Saudi prisoner was distraught over a possible death sentence for charges later dropped by the Pentagon.  Mohammed al-Qahtani cut himself at least three times and had to be hospitalized at the U.S. Navy base in Cuba, attorney Gitanjali Gutierrez said. Al-Qahtani made the suicide attempt after learning military prosecutors filed capital charges against him and five other Guantanamo prisoners for their alleged roles in the Sept. 11 terrorist attacks.