20th hijacker is a possible additional terrorist in the September 11 attacks of 2001 who , for whatever reason , was not able to participate . The 20th hijacker , though not present during the actual attacks , is said to have been deeply involved in the preparations . There were many variations of the 9/11 plot , with the number of terrorists fluctuating with available resources and changing circumstances . In the end , there were 19 hijackers : three of the planes were taken over by five members each and the fourth was hijacked by four people . The latter plane , United Airlines Flight 93 , was unsuccessful in its mission – instead of hitting any targets in Washington , D.C. , it simply crashed into a field near Shanksville , Pennsylvania , due to resistance from passengers . Thus , the idea of a 20th hijacker came to be widely discussed
United Airlines Flight 93
United Airlines Flight 93
20th hijacker