20th hijacker The 20th hijacker is a possible additional terrorist in the September 11 , 2001 , attacks who was not able to participate . 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 only four people . One plane , United Airlines Flight 93 , had fewer hijackers than the rest and was also less successful in its mission - instead of hitting any of the obvious targets in Washington , D . C . , it crashed into a field near Shanksville , Pennsylvania , due to resistance from passengers . Thus the idea of a 20th hijacker came to be widely discussed . Hijackers . The 9 / 11 Commission concluded that Khalid Sheikh Mohammed had intended to have as many as 25 or 26 hijackers for the plot . It was also reported that 14 members of al - Qaeda , in addition to the 19 known hijackers , had attempted to enter the United States to participate in the attacks . Ramzi bin al - Shibh allegedly meant to take part in the attacks , but he was repeatedly denied a visa for entry into the US . Mohamed al - Kahtani , a Saudi Arabian citizen , is often referred to as the 20th hijacker . José Meléndez - Pérez , a US Immigration inspector at Orlando International Airport refused his entry into the US in August 2001 . He was later captured in Afghanistan and imprisoned at the US military prison known as Camp X - Ray at Guantanamo Bay , Cuba . In January 2009 , Susan J . Crawford asserted that Kahtani ' s interrogation at Camp X - Ray amounted to torture . Zacarias Moussaoui was considered as a replacement for Ziad Jarrah , who at one point threatened to withdraw from the scheme because of tensions amongst the plotters . Plans to include Moussaoui were never finalized , as the al - Qaeda hierarchy had doubts about his reliability . Ultimately , Moussaoui did not play a role in the hijacking scheme . He was arrested about four weeks before the attacks . The other al - Qaeda members who allegedly attempted , but were not able , to take part in the attacks were Saeed al - Ghamdi ( not to be confused with the successful hijacker of the same name ) , Tawfiq bin Attash , Ali Abdul Aziz Ali , Mushabib al - Hamlan , Zakariyah Essabar , Saeed Ahmad al - Zahrani , Ali Abd al - Rahman al - Faqasi al - Ghamdi , Saeed al - Baluchi , Qutaybah al - Najdi , Zuhair al - Thubaiti , and Saud al - Rashi . Khalid Sheikh Mohammed , the attack ' s alleged mastermind , had wanted to remove at least one member — Khalid al - Mihdhar — from the operation , but he was overruled by Osama bin Laden . According to the BBC , Fawaz al - Nashimi claimed to have been the " 20th hijacker " . An Al - Qaeda video has been released from a US intelligence organization , showing al - Nashimi justifying attacks on the west . The U . S dismissed al - Nashimi ' s claims as propaganda . He was also known as Turki bin Fuheid al - Muteiry and took part in a May 29 , 2004 attack on oil facilities in Khobar , Saudi Arabia . He was killed in a June 2004 shootout with Saudi Arabian security forces . In fiction . The Saudi novelist Abdullah Thabit has written a bestselling novel titled " Terrorist Number 20 " ( 2006 ) . The book recalls his teenage years as a religious extremist and was inspired in part by Ahmad Alnami , one of the 9 / 11 hijackers and a fellow resident of Abha who was vaguely familiar to Thabit . In April 2006 , three months after the release of the book , Thabit was forced to move from Abha to Jeddah with his family after receiving death threats from Islamic radicals .