He arrived in the United States in May 2001 on a tourist visa and helped plan out how the attacks would take place . On September 11 , 2001 , he boarded United Airlines Flight 175 and assisted in the hijacking of the plane so that lead hijacker and trained pilot Marwan al-Shehhi could take over the plane and crash it into the South Tower of the World Trade Center , as part of the coordinated attacks
United Airlines Flight 175
United Airlines Flight 175
Ahmed al-Ghamdi