20th hijacker

The 20th hijacker is a possible additional terrorist in the September 11 attacks who, for unknown reasons, was unable 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, crashed into a field near Shanksville, Pennsylvania, due to the resistance from passengers before it could reach its target in Washington, D.C.

Suspects

Various people associated with Al-Qaeda have either claimed or have been speculated as the possible 20th hijacker in the September 11 attacks. thumb|[[Mohammed al-Qahtani during his imprisonment at the Guantanamo Bay detention camp .]]

Mohammed al-Qahtani

Investigators have accused Mohammed al-Qahtani, a Saudi national, of being the intended 20th hijacker, and intending to board Flight 93 as its fifth hijacker (and fourth muscle hijacker) on September 11. These allegations stem from circumstances surrounding al-Qahtani's failed attempt to enter the United States shortly before the September 11 attacks.

Having originally flown out of Dubai on August 3, 2001, al-Qahtani had disembarked a Virgin Atlantic flight from London Gatwick Airport and arrived at Orlando International Airport the following day. With a one-way ticket and $2,800 in cash, al-Qahtani was questioned by immigration agent José Meléndez-Pérez on suspicion of being an illegal immigrant. Al-Qahtani had been stopped by another immigration agent before Meléndez-Pérez, but al-Qahtani could not communicate with the agent nor did he properly fill out necessary travel documents. Meléndez-Pérez described that upon being questioned via an interpreter employed by the Department of Justice, al-Qahtani was belligerent and frequently changed his reasons for arriving to Orlando. Before being deported, al-Qahtani was photographed and fingerprinted through INSPASS. Meléndez-Pérez later testified that al-Qahtani had turned to him and another inspector and said "I'll be back." in English before boarding his return flight. According to the FBI, Atta did not leave the airport's parking lot until it was confirmed al-Qahtani was returning to Dubai. According to author Jane Mayer, investigators could not pinpoint al-Qahtani's identity until July 2002, when a routine fingerprint analysis matched with al-Qahtani's fingerprints taken in Orlando.

On March 3 2006, Time magazine published a leaked log detailing 49 days of al-Qahtani's interrogations at Guantanamo Bay detention camp from November 23 2002 to January 11 2003. Crawford's statement was the first time any official of the Bush administration had publicly described the treatment of detainees at Guantanamo as torture.

On March 6 2022, al-Qahtani was airlifted from Guantanamo by the US military and flown back to Saudi Arabia to a mental health treatment facility after 20 years in American custody. His release was announced by the US Department of Defense the next day.

9/11 Commission's findings

In the 9/11 Commission's final report, al-Qahtani is first introduced as "The operative likely intended to round out the team for [United 93]". The 9/11 Commission reported that in a purported conversation between Mohamed Atta and Ramzi bin al-Shibh, the two referred to al-Qahtani as "the friend who is coming as a tourist" whom Mustafa al-Hawsawi was sending as “the last one” to “complete the group.”

thumb|200x200px|Mugshot of Moussaoui, 2006

Zacarias Moussaoui

Zacarias Moussaoui, a French citizen of Moroccan origin, has widely been referred to as the 20th hijacker. French intelligence began tracking Moussaoui in 1996, after he was spotted with Islamic extremists in London. Intelligence officials stated that Moussaoui had flown to Afghanistan multiple times to attend terrorist training camps and meet with Al-Qaeda officials in Kandahar and Jalalabad. Moussaoui may have been considered as a replacement for Ziad Jarrah, who at one point threatened to withdraw from the scheme because of tensions amongst the plotters. The 9/11 Commission stated that Moussaoui received money and information from the principal architect of the attacks, Khalid Sheikh Mohammed (KSM), throughout its planning stages. An audio recording attributed to Osama bin Laden said in translation that Moussaoui "had no connection at all with 11 September... I am the one in charge of the 19 brothers and I never assigned brother Zacarias to be with them in that mission ... Since Zacarias Moussaoui was still learning to fly, he wasn't number 20 in the group, as your government claimed". The voice alleged to be bin Laden also suggested that Moussaoui's confession was "void" as it was a result of pressures applied during his incarceration. Conversely, the 9/11 Commission remarked that had the FBI known about Moussaoui's connection with Al-Qaeda earlier, the US might conceivably have disrupted or derailed the 9/11 attacks altogether. Despite 57 hours of flying lessons, Moussaoui failed and left without ever having flown solo. In August 2001, Moussaoui began taking flying lessons at Pan-Am International Flight Academy in Eagan, Minnesota. Moussaoui had been wired thousands of dollars to fund his training, and he paid the bulk of his tuition in US$100 bills. According to his classmates and instructor in Eagan, Moussaoui was immediately viewed with suspicion due to his aggression and unusual interest in flying wide-body aircraft such as a Boeing 747-400 despite his lack of experience. Moussaoui is currently held at the ADX Florence federal supermax prison in Colorado.

thumb|200x200px|Bin al-Shibh, circa 2023

Ramzi bin al-Shibh

Ramzi bin al-Shibh was one of the first people to be labeled as the "20th hijacker" by US authorities. Bin al-Shibh meant to take part in the attacks and may have been the intended hijacker-pilot of American Airlines Flight 77, but he was repeatedly denied a visa for entry into the US. His role as one of the four hijacker-pilots preceded Hani Hanjour, as original plans for the 9/11 attacks called for bin al-Shibh to be one of the hijacker pilots along with Mohamed Atta, Marwan al-Shehhi, and Ziad Jarrah. Unlike Hanjour, bin al-Shibh was a member of the Hamburg cell alongside the three other hijacker pilots. After failing to gain a visa to enter the United States, bin al-Shibh served as an intermediary between Atta in the United States and KSM in Afghanistan. The 9/11 Commission noted that Bin al-Shibh had arranged to wire funding for the plot, including Moussaoui's tuition money.

Capture and trial

Bin al-Shibh has been in United States custody since he was captured in Karachi, Pakistan in 2002. He was held by the Central Intelligence Agency (CIA) before being transferred to Guantanamo Bay in 2006. While in custody, Bin al-Shibh underwent enhanced interrogation techniques. Finally charged in 2008 before a military commission, he and four other accused planners of 9/11: KSM, Ammar al-Baluchi, Mustafa al-Hawsawi, and Walid bin Attash were jointly prosecuted and went to trial beginning in May 2012. In 2023, a US military judge ruled him too psychologically damaged to defend himself after the torture he sustained while in the custody of the CIA and Guantanamo Bay. In January 2026, a military judge rejected a government request to restart death-penalty proceedings against bin al-Shibh.

Fawaz al-Nashimi

According to the BBC, Fawaz al-Nashimi, also known as Turki bin Fuheid al-Muteiry, claimed to have been the "20th hijacker". Al-Nashimi 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.

Other possible candidates

According to the 9/11 Commission, other individuals who allegedly attempted, but were not able, to take part in the attacks were Walid bin Attash, Zakariya Essabar, Abu Bara al Yemeni, Ali Abdul Aziz Ali, Mushabib al-Hamlan, Abderraouf Jdey, Khalid 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.

In addition, Khalid Sheikh Mohammed, the attack's mastermind, had wanted to remove Khalid al-Mihdhar from the operation, but he was overruled by Osama bin Laden.

In popular culture

The Saudi Arabian novelist Abdullah Thabit wrote a 2006 novel titled Terrorist Number 20 that became a bestseller. The book recalls his teenage years as a religious extremist and was inspired in part by Ahmed al-Nami, 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.