September 11 attacks

September 11 attacks
Part of terrorism in the United States
A montage of eight images depicting, from top to bottom, the World Trade Center towers burning, the collapsed section of the Pentagon, the impact explosion in the South Tower, a rescue worker standing in front of rubble of the collapsed towers, an excavator unearthing a smashed jet engine, three frames of video depicting American Airlines Flight 77 hitting the Pentagon

DateSeptember 11, 2001; 17 years ago (2001-09-11)
8:46 a.m. – 10:28 a.m. (EDT)
Attack type
Deaths2,996 (2,977 victims + 19 hijackers)
Non-fatal injuries
No. of participants

The September 11 attacks (also referred to as 9/11)[a] were a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda[2][3][4] against the United States on the morning of Tuesday, September 11, 2001. The attacks killed 2,996 people, injured over 6,000 others, and caused at least $10 billion in infrastructure and property damage.[5][6] Additional people died of 9/11-related cancer and respiratory diseases in the months and years following the attacks.

Four passenger airliners operated by two major U.S. passenger air carriers (United Airlines and American Airlines)—all of which departed from airports in the northeastern United States bound for California—were hijacked by 19 al-Qaeda terrorists. Two of the planes, American Airlines Flight 11 and United Airlines Flight 175, were crashed into the North and South towers, respectively, of the World Trade Center complex in Lower Manhattan. Within an hour and 42 minutes, both 110-story towers collapsed. Debris and the resulting fires caused a partial or complete collapse of all other buildings in the World Trade Center complex, including the 47-story 7 World Trade Center tower, as well as significant damage to ten other large surrounding structures. A third plane, American Airlines Flight 77, was crashed into the Pentagon (the headquarters of the U.S. Department of Defense) in Arlington County, Virginia, which led to a partial collapse of the building's west side. The fourth plane, United Airlines Flight 93, was initially flown toward Washington, D.C., but crashed into a field in Stonycreek Township near Shanksville, Pennsylvania, after its passengers thwarted the hijackers. 9/11 is the single deadliest terrorist attack in human history and the single deadliest incident for firefighters and law enforcement officers[7] in the history of the United States, with 343 and 72 killed, respectively.

Suspicion quickly fell on al-Qaeda. The United States responded by launching the War on Terror and invaded Afghanistan to depose the Taliban, which had failed to comply with U.S. demands to extradite Osama bin Laden and expel al-Qaeda from Afghanistan. Many countries strengthened their anti-terrorism legislation and expanded the powers of law enforcement and intelligence agencies to prevent terrorist attacks. Although Osama bin Laden, al-Qaeda's leader, initially denied any involvement, in 2004 he claimed responsibility for the attacks.[1] Al-Qaeda and bin Laden cited U.S. support of Israel, the presence of U.S. troops in Saudi Arabia, and sanctions against Iraq as motives. After evading capture for almost a decade, bin Laden was located in Pakistan and killed by SEAL Team Six of the U.S. Navy in May 2011.

The destruction of the World Trade Center and nearby infrastructure seriously harmed the economy of Lower Manhattan and had a significant effect on global markets, which resulted in the closing of Wall Street until September 17 and the civilian airspace in the U.S. and Canada until September 13. Many closings, evacuations, and cancellations followed, out of respect or fear of further attacks. Cleanup of the World Trade Center site was completed in May 2002, and the Pentagon was repaired within a year. On November 18, 2006, construction of One World Trade Center began at the World Trade Center site. The building was officially opened on November 3, 2014.[8][9] Numerous memorials have been constructed, including the National September 11 Memorial & Museum in New York City, the Pentagon Memorial in Arlington County, Virginia, and the Flight 93 National Memorial in a field in Stonycreek Township near Shanksville, Pennsylvania.



The origins of al-Qaeda can be traced to 1979 when the Soviet Union invaded Afghanistan. Osama bin Laden traveled to Afghanistan and helped organize Arab mujahideen to resist the Soviets.[10] Under the guidance of Ayman al-Zawahiri, bin Laden became more radical.[11] In 1996, bin Laden issued his first fatwā, calling for American soldiers to leave Saudi Arabia.[12]

In a second fatwā in 1998, bin Laden outlined his objections to American foreign policy with respect to Israel, as well as the continued presence of American troops in Saudi Arabia after the Gulf War.[13] Bin Laden used Islamic texts to exhort Muslims to attack Americans until the stated grievances are reversed. Muslim legal scholars "have throughout Islamic history unanimously agreed that the jihad is an individual duty if the enemy destroys the Muslim countries", according to bin Laden.[13]

Osama bin Laden

Osama bin Laden at about 40 years of age, 1997

Bin Laden orchestrated the attacks and initially denied involvement but later recanted his false statements.[1][14][15] Al Jazeera broadcast a statement by bin Laden on September 16, 2001, stating, "I stress that I have not carried out this act, which appears to have been carried out by individuals with their own motivation."[16] In November 2001, U.S. forces recovered a videotape from a destroyed house in Jalalabad, Afghanistan. In the video, bin Laden is seen talking to Khaled al-Harbi and admits foreknowledge of the attacks.[17] On December 27, 2001, a second bin Laden video was released. In the video, he said:

It has become clear that the West in general and America in particular have an unspeakable hatred for Islam. ... It is the hatred of crusaders. Terrorism against America deserves to be praised because it was a response to injustice, aimed at forcing America to stop its support for Israel, which kills our people. ... We say that the end of the United States is imminent, whether Bin Laden or his followers are alive or dead, for the awakening of the Muslim umma (nation) has occurred

but he stopped short of admitting responsibility for the attacks.[18] The transcript refers several times to the United States specifically targeting Muslims.

Shortly before the U.S. presidential election in 2004, bin Laden used a taped statement to publicly acknowledge al-Qaeda's involvement in the attacks on the United States. He admitted his direct link to the attacks and said they were carried out because:

we are free ... and want to regain freedom for our nation. As you undermine our security, we undermine yours.[19]

Bin Laden said he had personally directed his followers to attack the World Trade Center and the Pentagon.[20][21] Another video obtained by Al Jazeera in September 2006 shows bin Laden with Ramzi bin al-Shibh, as well as two hijackers, Hamza al-Ghamdi and Wail al-Shehri, as they make preparations for the attacks.[22] The U.S. never formally indicted bin Laden for the 9/11 attacks but he was on the FBI's Most Wanted List for the bombings of the U.S. Embassies in Dar es Salaam, Tanzania, and Nairobi, Kenya.[23][24] After a 10-year manhunt, bin Laden was killed by American special forces in a compound in Abbottabad, Pakistan on May 2, 2011.[25][26]

Khalid Sheikh Mohammed

Khalid Sheikh Mohammed after his capture in 2003

Journalist Yosri Fouda of the Arabic television channel Al Jazeera reported that, in April 2002, Khalid Sheikh Mohammed admitted his involvement, along with Ramzi bin al-Shibh.[27][28][29] The 9/11 Commission Report determined that the animosity towards the United States felt by Mohammed, the principal architect of the 9/11 attacks, stemmed from his "violent disagreement with U.S. foreign policy favoring Israel".[30] Mohammed was also an adviser and financier of the 1993 World Trade Center bombing and the uncle of Ramzi Yousef, the lead bomber in that attack.[31][32]

Mohammed was arrested on March 1, 2003, in Rawalpindi, Pakistan, by Pakistani security officials working with the CIA. He was then held at multiple CIA secret prisons and Guantanamo Bay where he was interrogated and tortured with methods including waterboarding.[33][34][35] During U.S. hearings at Guantanamo Bay in March 2007, Mohammed again confessed his responsibility for the attacks, stating he "was responsible for the 9/11 operation from A to Z" and that his statement was not made under duress.[29][36]

Other al-Qaeda members

In "Substitution for Testimony of Khalid Sheikh Mohammed" from the trial of Zacarias Moussaoui, five people are identified as having been completely aware of the operation's details. They are bin Laden, Khalid Sheikh Mohammed, Ramzi bin al-Shibh, Abu Turab al-Urduni, and Mohammed Atef.[37] To date, only peripheral figures have been tried or convicted for the attacks.

On September 26, 2005, the Spanish high court sentenced Abu Dahdah to 27 years in prison for conspiracy on the 9/11 attacks and being a member of the terrorist organization al-Qaeda. At the same time, another 17 al-Qaeda members were sentenced to penalties of between six and eleven years.[38] On February 16, 2006, the Spanish Supreme Court reduced the Abu Dahdah penalty to 12 years because it considered that his participation in the conspiracy was not proven.[39]

Also in 2006, Moussaoui—who some originally suspected might have been the assigned 20th hijacker—was convicted for the lesser role of conspiracy to commit acts of terrorism and air piracy. He was sentenced to life without parole in the United States.[40][41] Mounir el-Motassadeq, an associate of the Hamburg-based hijackers, served 15 years in Germany for his role in helping the hijackers prepare for the attacks. He was released in October 2018, and deported to Morocco.[42]

The Hamburg cell in Germany included radical Islamists who eventually came to be key operatives in the 9/11 attacks.[43] Mohamed Atta, Marwan al-Shehhi, Ziad Jarrah, Ramzi bin al-Shibh, and Said Bahaji were all members of al-Qaeda's Hamburg cell.[44]


Osama bin Laden's declaration of a holy war against the United States, and a 1998 fatwā signed by bin Laden and others, calling for the killing of Americans,[13] are seen by investigators as evidence of his motivation.[45] In bin Laden's November 2002 "Letter to America", he explicitly stated that al-Qaeda's motives for their attacks include:

After the attacks, bin Laden and al-Zawahiri released additional videotapes and audio recordings, some of which repeated those reasons for the attacks. Two particularly important publications were bin Laden's 2002 "Letter to America",[49] and a 2004 videotape by bin Laden.[50]

Bin Laden interpreted Muhammad as having banned the "permanent presence of infidels in Arabia".[51] In 1996, bin Laden issued a fatwā calling for American troops to leave Saudi Arabia. In 1998, al-Qaeda wrote, "for over seven years the United States has been occupying the lands of Islam in the holiest of places, the Arabian Peninsula, plundering its riches, dictating to its rulers, humiliating its people, terrorizing its neighbors, and turning its bases in the Peninsula into a spearhead through which to fight the neighboring Muslim peoples."[52]

In a December 1999 interview, bin Laden said he felt that Americans were "too near to Mecca", and considered this a provocation to the entire Muslim world.[53] One analysis of suicide terrorism suggested that without U.S. troops in Saudi Arabia, al-Qaeda likely would not have been able to get people to commit to suicide missions.[54]

In the 1998 fatwā, al-Qaeda identified the Iraq sanctions as a reason to kill Americans, condemning the "protracted blockade"[52] among other actions that constitute a declaration of war against "Allah, his messenger, and Muslims."[52] The fatwā declared that "the ruling to kill the Americans and their allies – civilians and military – is an individual duty for every Muslim who can do it in any country in which it is possible to do it, in order to liberate the al-Aqsa Mosque and the holy mosque of Mecca from their grip, and in order for their [the Americans'] armies to move out of all the lands of Islam, defeated and unable to threaten any Muslim."[13][55]

In 2004, Bin Laden claimed that the idea of destroying the towers had first occurred to him in 1982, when he witnessed Israel's bombardment of high-rise apartment buildings during the 1982 Lebanon War.[56][57] Some analysts, including Mearsheimer and Walt, also claimed that U.S. support of Israel was one motive for the attacks.[47][53] In 2004 and 2010, bin Laden again connected the September 11 attacks with U.S. support of Israel, although most of the letter expressed bin Laden's disdain for President Bush and bin Laden's hope to "destroy and bankrupt" the U.S.[58][59]

Other motives have been suggested in addition to those stated by bin Laden and al-Qaeda, including western support of Islamic and non-Islamic authoritarian regimes in Saudi Arabia, Iran, Egypt, Iraq, Pakistan and northern Africa, and the presence of western troops in some of these countries.[60][page needed] Some authors suggested the "humiliation" that resulted from the Islamic world falling behind the Western world – this discrepancy was rendered especially visible by the globalization trend[61][62] and a desire to provoke the U.S. into a broader war against the Islamic world in the hope of motivating more allies to support al-Qaeda. Similarly, others have argued that 9/11 was a strategic move with the objective of provoking America into a war that would incite a pan-Islamic revolution.[63][64]


ground zero and surrounding area as seen from directly above depicting where the two planes impacted the towers
Map showing the attacks on the World Trade Center (the planes are not drawn to scale)

The idea for the attacks came from Khalid Sheikh Mohammed, who first presented it to Osama bin Laden in 1996.[65] At that time, bin Laden and al-Qaeda were in a period of transition, having just relocated back to Afghanistan from Sudan.[66] The 1998 African Embassy bombings and bin Laden's 1998 fatwā marked a turning point, as bin Laden became intent on attacking the United States.[66]

In late 1998 or early 1999, bin Laden gave approval for Mohammed to go forward with organizing the plot. A series of meetings occurred in early 1999, involving Mohammed, bin Laden, and his deputy Mohammed Atef.[66] Atef provided operational support for the plot, including target selections and helping arrange travel for the hijackers.[66] Bin Laden overruled Mohammed, rejecting some potential targets such as the U.S. Bank Tower in Los Angeles because "there was not enough time to prepare for such an operation".[67][68]

Diagram showing the attacks on the World Trade Center

Bin Laden provided leadership and financial support for the plot, and was involved in selecting participants.[69] Bin Laden initially selected Nawaf al-Hazmi and Khalid al-Mihdhar, both experienced jihadists who had fought in Bosnia. Hazmi and Mihdhar arrived in the United States in mid-January 2000. In spring 2000, Hazmi and Mihdhar took flying lessons in San Diego, California, but both spoke little English, performed poorly with flying lessons, and eventually served as secondary – or "muscle" – hijackers.[70][71]

In late 1999, a group of men from Hamburg, Germany arrived in Afghanistan; the group included Mohamed Atta, Marwan al-Shehhi, Ziad Jarrah, and Ramzi bin al-Shibh.[72] Bin Laden selected these men because they were educated, could speak English, and had experience living in the West.[73] New recruits were routinely screened for special skills and al-Qaeda leaders consequently discovered that Hani Hanjour already had a commercial pilot's license.[74] Mohammed later said that he helped the hijackers blend in by teaching them how to order food in restaurants and dress in Western clothing.[75]

Hanjour arrived in San Diego on December 8, 2000, joining Hazmi.[76]:6–7 They soon left for Arizona, where Hanjour took refresher training.[76]:7 Marwan al-Shehhi arrived at the end of May 2000, while Atta arrived on June 3, 2000, and Jarrah arrived on June 27, 2000.[76]:6 Bin al-Shibh applied several times for a visa to the United States, but as a Yemeni, he was rejected out of concerns he would overstay his visa and remain as an illegal immigrant.[76]:4, 14 Bin al-Shibh stayed in Hamburg, providing coordination between Atta and Mohammed.[76]:16 The three Hamburg cell members all took pilot training in South Florida.[76]:6

In spring of 2001, the secondary hijackers began arriving in the United States.[77] In July 2001, Atta met with bin al-Shibh in Spain, where they coordinated details of the plot, including final target selection. Bin al-Shibh also passed along bin Laden's wish for the attacks to be carried out as soon as possible.[78] Some of the hijackers received passports from corrupt Saudi officials who were family members, or used fraudulent passports to gain entry.[79]

Prior intelligence

In late 1999, al-Qaeda associate Walid bin Attash ("Khallad") contacted Mihdhar, telling him to meet him in Kuala Lumpur, Malaysia; Hazmi and Abu Bara al Yemeni would also be in attendance. The NSA intercepted a telephone call mentioning the meeting, Mihdhar, and the name "Nawaf" (Hazmi). While the agency feared that "Something nefarious might be afoot", it took no further action. The CIA had already been alerted by Saudi intelligence to the status of Mihdhar and Hazmi as al-Qaeda members, and a CIA team broke into Mihdhar's Dubai hotel room and discovered that Mihdhar had a U.S. visa. While Alec Station alerted intelligence agencies worldwide about this fact, it did not share this information with the FBI. The Malaysian Special Branch observed the January 5, 2000, meeting of the two al-Qaeda members, and informed the CIA that Mihdhar, Hazmi, and Khallad were flying to Bangkok, but the CIA never notified other agencies of this, nor did it ask the State Department to put Mihdhar on its watchlist. An FBI liaison to Alec Station asked permission to inform the FBI of the meeting, but was told that "'This is not a matter for the FBI.'"[80]

By late June, senior counter-terrorism official Richard Clarke and CIA director George Tenet were "convinced that a major series of attacks was about to come", although the CIA believed that the attacks would likely occur in Saudi Arabia or Israel.[81] In early July, Clarke put domestic agencies on "full alert", telling them that "Something really spectacular is going to happen here ... soon." He asked the FBI and the State Department to alert the embassies and police departments, and the Defense Department to go to "Threat Condition Delta."[82][83] Clarke would later write that "Somewhere in CIA there was information that two known al Qaeda terrorists had come into the United States. ... in [the] FBI there was information that strange things had been going on at flight schools in the United States. ... They had specific information about individual terrorists. ... None of that information got to me or the White House."[84]

On July 13, Tom Wilshire, a CIA agent assigned to the FBI's international terrorism division, emailed his superiors at the CIA's Counterterrorism Center (CTC), requesting permission to inform the FBI that Hazmi was in the country and that Mihdhar had a U.S. visa. The CIA never responded.[85]

The same day in July, Margarette Gillespie, an FBI analyst working in the CTC, was told to review material about the Malaysia meeting. She was not told of the participants' presence in the U.S. The CIA gave Gillespie surveillance photos of Mihdhar and Hazmi from the meeting to show to FBI counterterrorism, but did not tell her their significance. The Intelink database informed her not to share intelligence material on the meeting to criminal investigators. When shown the photos, the FBI were refused more details on their significance, and also did not receive Mihdhar's date of birth or passport number.[86] In late August 2001, Gillespie told the INS, the State Department, the Customs Service, and the FBI to put Hazmi and Mihdhar on their watchlists, but the FBI was prohibited from using criminal agents in the search for the duo, which hindered their efforts.[87]

Also in July, a Phoenix-based FBI agent sent a message to FBI headquarters, Alec Station, and to FBI agents in New York, alerting them to "the possibility of a coordinated effort by Osama bin Laden to send students to the United States to attend civil aviation universities and colleges." The agent, Kenneth Williams, suggested the need to interview all flight school managers and identify all Arab students seeking flight training.[88] In July, Jordan alerted the U.S. that al-Qaeda was planning an attack on the U.S.; "months later", Jordan notified the U.S. that the attack's codename was "The Big Wedding", and that it involved airplanes.[89]

On August 6, 2001, the CIA's Presidential Daily Brief, designated "For the President Only", was entitled "Bin Ladin Determined to Strike in U.S." The memo noted that "The FBI information ... indicates patterns of suspicious activity in this country consistent with preparations for hijackings or other types of attacks."[90]

In mid-August, one Minnesota flight school alerted the FBI to Zacarias Moussaoui, who had asked "suspicious questions." The FBI found that he was a radical who had traveled to Pakistan, and the INS arrested him for overstaying his French visa. Their request to search his laptop was denied by FBI headquarters due to the lack of probable cause.[91]

The failures in intelligence-sharing were attributed to 1995 Justice Department policies limiting intelligence sharing, combined with CIA and NSA reluctance in revealing "sensitive sources and methods" such as tapped phones.[92] Testifying before the 9/11 Commission in April 2004, then-Attorney General John Ashcroft recalled that the "single greatest structural cause for the September 11th problem was the wall that segregated or separated criminal investigators and intelligence agents."[93] Clarke also wrote that "There were failures in the organizations ... failures to get information to the right place at the right time."[94]

Other Languages
Bân-lâm-gú: 911 Sū-kiāⁿ
беларуская (тарашкевіца)‎: Тэрарыстычныя акты 11 верасьня 2001 году
Gaeilge: 9/11
Gàidhlig: 9/11
한국어: 9·11 테러
Bahasa Indonesia: Serangan 11 September 2001
Кыргызча: 11 сентябрь 2001
پنجابی: 9/11
Simple English: September 11 attacks
srpskohrvatski / српскохрватски: Napadi 11. septembra 2001.
Tiếng Việt: Sự kiện 11 tháng 9
ייִדיש: 9/11
粵語: 911事件