How many years of prison was Mounir el - Motassadeq sentenced to for the September 11 hijacking ?
Important members included Mohamed Atta , who led the four hijacking teams in 2001 and piloted American Airlines Flight 11 ; Ramzi bin al - Shibh , who conspired with the other three members but was unable to enter the United States ; and Marwan al - Shehhi , who piloted United Airlines Flight 175 .