11 September 2001 attacks

The September 11 attacks, commonly known as 9/11, were four coordinated suicide terrorist attacks carried out by al-Qaeda against the United States on Tuesday, September 11, 2001. That morning, nineteen terrorists hijacked four commercial airliners scheduled to travel from the Northeastern United States to California. The hijackers crashed the first two planes into the Twin Towers of the World Trade Center in New York City, and the third plane into the Pentagon (the headquarters of the United States military) in Arlington County, Virginia. The fourth plane was intended to hit a federal government building in Washington, D.C., but crashed in a field following a passenger revolt. The attacks killed nearly 3,000 people and instigated the war on terror.

The first impact was that of American Airlines Flight 11. It was crashed into the North Tower of the World Trade Center complex in Lower Manhattan at 8:46 a.m. Seventeen minutes later, at 9:03, the World Trade Center’s South Tower was hit by United Airlines Flight 175. Both 110-story skyscrapers collapsed within an hour and forty-two minutes, precipitating the collapse of other World Trade Center structures including 7 World Trade Center, and damaging nearby buildings. A third flight, American Airlines Flight 77, crashed into the west side of the Pentagon in Arlington County, Virginia, at 9:37 a.m., causing a partial collapse. The fourth and final flight, United Airlines Flight 93, flew in the direction of Washington, D.C. Alerted of the previous attacks, the plane's passengers fought back in an attempt to gain control of the aircraft, but the hijackers ultimately crashed the plane in a field in Stonycreek Township, Pennsylvania, near Shanksville at 10:03 a.m. Investigators determined that Flight 93 was targeting either the United States Capitol or the White House.

Within hours of the attacks, the Central Intelligence Agency determined that al-Qaeda was responsible. The United States formally responded by launching the war on terror and invading Afghanistan to depose the Taliban, which had not complied with U.S. demands to expel al-Qaeda from Afghanistan and extradite its leader, Osama bin Laden. The U.S.'s invocation of Article 5 of NATO—its only usage to date—called upon allies to fight al-Qaeda. As U.S. and NATO ground forces swept through Afghanistan, bin Laden went into hiding. Although bin Laden denied any involvement, in 2004 he formally claimed responsibility for the attacks. Al-Qaeda's cited motivations included U.S. support of Israel, the presence of U.S. troops in Saudi Arabia, and sanctions against Iraq. After evading capture for almost a decade, bin Laden was killed by the U.S. military on May 2, 2011.

The attacks resulted in 2,977 non-hijacker fatalities, an indeterminate number of injuries, and substantial long-term health consequences, in addition to at least $10billion in infrastructure and property damage. It remains the deadliest terrorist attack in human history and the single deadliest incident for firefighters and law enforcement officers in U.S. history, with 343 and 72 killed, respectively. The destruction of the World Trade Center and its environs seriously harmed the New York City economy and induced global market shocks. Many other countries strengthened anti-terrorism legislation and expanded their powers of law enforcement and intelligence agencies. Cleanup of the World Trade Center site (colloquially "Ground Zero") took eight months and was completed in May 2002, while the Pentagon was repaired within a year. After delays in the design of a replacement complex, the One World Trade Center began construction in November 2006 and opened in November 2014. Memorials to the attacks include the National September 11 Memorial & Museum in New York City, the Pentagon Memorial in Arlington County, and the Flight 93 National Memorial at the Pennsylvania crash site.

Background

Al-Qaeda

The origins of al-Qaeda can be traced to 1979 when the Soviet Union invaded Afghanistan. Osama bin Laden traveled to the central Asian country to volunteer, viewing the war as a holy cause to help fellow Muslims (in Afghanistan) defeat Communist invaders (the Soviets). Bin Laden organized fellow Arab mujahideen (the " Afghan Arabs") to resist the Soviets until that country's exit from Afghanistan in 1989. The U.S. Central Intelligence Agency (CIA) funneled several billion dollars worth of weapons to the indigenous Afghan mujahideen resistance, a portion of which bled to the Arab volunteers. However, no direct U.S. aid to bin Laden or any of his affiliates has ever been established.

In 1996, bin Laden issued his first '' fatwā'', calling for American soldiers to leave Saudi Arabia. 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. Bin Laden used Islamic texts to exhort Muslims to attack Americans until the stated grievances were 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.

Osama bin Laden

Bin Laden orchestrated the attacks. He initially denied involvement, but later recanted his false statements. Al Jazeera broadcast a statement by him on September 16, 2001: "I stress that I have not carried out this act, which appears to have been carried out by individuals with their own motivation." 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. On December 27, 2001, a second bin Laden video was released. In the video, he said:

but he stopped short of admitting responsibility for the attacks.

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...

Bin Laden said he had personally directed his followers to attack the World Trade Center and the Pentagon. Another video obtained by Al Jazeera in September 2006 shows bin Laden with one of the attacks' chief planners, Ramzi bin al-Shibh, as well as two hijackers, Hamza al-Ghamdi and Wail al-Shehri, as they made preparations for the attacks. 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. After a 10-year manhunt, U.S. President Barack Obama announced that bin Laden was killed by American special forces in his compound in Abbottabad, Pakistan, on May 1, 2011.

Khalid Sheikh Mohammed

Journalist Yosri Fouda of the Arabic television channel Al Jazeera reported that in April 2002 al-Qaeda member Khalid Sheikh Mohammed admitted his involvement in the attacks, along with Ramzi bin al-Shibh. The 2004 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".9/11 Commission Report (2004), p. 147. 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.

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. 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.

A letter presented by Mohammed's lawyers in the U.S. District Court, Manhattan, on July 26, 2019, indicated that he was interested in testifying about Saudi Arabia's role in the 9/11 attacks and helping the victims and families of the victims of 9/11 in exchange for the United States not seeking the death penalty against him. James Kreindler, one of the lawyers for the victims, raised question over the usefulness of his testimony.

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. 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. On February 16, 2006, the Spanish Supreme Court reduced Abu Dahdah's penalty to 12 years because it considered that his participation in the conspiracy was not proven.

Also in 2006 Moussaoui, who some originally suspected might have been the assigned twentieth hijacker, was convicted for the lesser role of conspiracy to commit acts of terrorism and air piracy. He was sentenced to life in prison without parole in the United States. 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.

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

Motives

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, are seen by investigators as evidence of his motivation.

In bin Laden's November 2002 "Letter to America", he explicitly stated that al-Qaeda's motives for their attacks include:
* U.S. support of Israel*Mearsheimer (2007), p. 67.
*Kushner (2003), p. 389.
*Murdico (2003), p. 64.
*Kelley (2006), p. 207.
*Ibrahim (2007), p. 276.
*
* Support for the "attacks against Muslims" in Somalia
* Support of Philippines against Muslims in the Moro conflict
* Support for Israeli "aggression" against Muslims in Lebanon
* Support of Russian "atrocities against Muslims" in Chechnya
* Pro-American governments in the Middle East (who "act as your agents") being against Muslim interests
* Support of Indian "oppression against Muslims" in Kashmir
* The presence of U.S. troops in Saudi Arabia
* The sanctions against Iraq*
*

After the attacks, bin Laden and Ayman 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" and a 2004 videotape by bin Laden.

Bin Laden interpreted Muhammad as having banned the "permanent presence of infidels in Arabia". 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."

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. 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.

In the 1998 ''fatwā'', al-Qaeda identified the Iraq sanctions as a reason to kill Americans, condemning the "protracted blockade" among other actions that constitute a declaration of war against "Allah, his messenger, and Muslims." The ''fatwā'' declared that "the ruling to kill the Americans and their alliescivilians and militaryis 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 he Americans'armies to move out of all the lands of Islam, defeated and unable to threaten any Muslim."

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. Some analysts, including political scientists John Mearsheimer and Stephen Walt, also claimed that U.S. support of Israel was one motive for the attacks. 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.

Other motives have been suggested in addition to those stated by bin Laden and al-Qaeda. Some authors suggested the "humiliation" that resulted from the Islamic world falling behind the Western worldthis discrepancy was rendered especially visible by globalization 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.

Documents seized during the 2011 operation that killed bin Laden included a few notes handwritten by bin Laden in September 2002 with the heading "The Birth of the Idea of September 11". In these notes he describes how he was inspired by the crash of EgyptAir Flight 990 on October 31, 1999, which was deliberately crashed by co-pilot Gameel Al-Batouti. "This is how the idea of 9/11 was conceived and developed in my head, and that is when we began the planning" bin Laden continued, adding that no one but Abu Hafs and Abu al-Khair knew about it at the time. The 9/11 Commission Report identified Khalid Sheikh Mohammed as the architect of 9/11, but he is not mentioned in bin Laden's notes.

Planning

The attacks were conceived by Khalid Sheikh Mohammed, who first presented it to Osama bin Laden in 1996. At that time, bin Laden and al-Qaeda were in a period of transition, having just relocated back to Afghanistan from Sudan.9/11 Commission Report (2004), Chapter 5, pp. ?? The 1998 African embassy bombings and bin Laden's February 1998 fatwā marked a turning point of al-Qaeda's terrorist operation, as bin Laden became intent on attacking the United States.

In late 1998 or early 1999, bin Laden gave approval for Mohammed to go forward with organizing the plot. Mohammed, bin Laden, and Mohammed Atef, the deputy of bin Laden, held a series of meetings in early 1999. Atef provided operational support, including target selections and helping arrange travel for the hijackers. Bin Laden overruled Mohammed, rejecting potential targets such as the U.S. Bank Tower in Los Angeles for lack of time.

Bin Laden provided leadership and financial support and was involved in selecting participants. He 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 early 2000, Hazmi and Mihdhar took flying lessons in San Diego, California, but both spoke little English; performed poorly in flying lessons; and eventually served as secondary ("muscle") hijackers.

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. Bin Laden selected these men because they were educated, could speak English, and had experience living in the West. New recruits were routinely screened for special skills and al-Qaeda leaders consequently discovered that Hani Hanjour already had a commercial pilot's license. Mohammed later said that he helped the hijackers blend in by teaching them how to order food in restaurants and dress in Western clothing.

Hanjour arrived in San Diego on December 8, 2000, joining Hazmi. They soon left for Arizona, where Hanjour took refresher training. Marwan al-Shehhi arrived at the end of May 2000, while Atta arrived on June 3, 2000, and Jarrah arrived on June 27, 2000. 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. Bin al-Shibh stayed in Hamburg, providing coordination between Atta and Mohammed. The three Hamburg cell members all took pilot training in South Florida at Huffman Aviation.

In the spring of 2001, the secondary hijackers began arriving in the United States. 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. Some of the hijackers received passports from corrupt Saudi officials who were family members or used fraudulent passports to gain entry.

There have been a few theories that 9/11 was selected by the hijackers as the date of the attack because of its resemblance to 9-1-1, the phone number used to report emergencies in the United States. However, Lawrence Wright wrote that the hijackers chose the date when John III Sobieski, the King of Poland and Grand Duke of Lithuania, began the battle which turned back the Ottoman Empire's Muslim armies that were attempting to capture Vienna on 11 September 1683. During 1683, Vienna was the seat of the Holy Roman Empire and Habsburg monarchy, both major powers in Europe at the time. For Osama bin Laden, this was a date when the West gained some dominance over Islam, and by attacking on this date, he hoped to make a step in Islam "winning" the war for worldwide power and influence.

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 "Something nefarious might be afoot", it took no further action.

The CIA had already been alerted by Saudi intelligence about 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: "This is not a matter for the FBI."

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 the attacks would likely occur in Saudi Arabia or Israel. In early July, Clarke put domestic agencies on "full alert", telling them "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". Clarke later wrote: "Somewhere in CIA there was information that two known al Qaeda terrorists had come into the United States. Somewhere in 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 from which one could have deduced what was about to happen. None of that information got to me or the White House."

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.

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 participant's 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 with criminal investigators. When shown the photos, the FBI were refused more details on their significance, and they were not given Mihdhar's date of birth nor passport number. 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 searching for the duo, hindering their efforts.

Also in July, a Phoenix-based FBI agent sent a message to FBI headquarters, Alec Station, and 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. 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 aeroplanes.

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

In mid-August, one Minnesota flight school alerted the FBI about Zacarias Moussaoui, who had asked "suspicious questions". The FBI found that Moussaoui 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.

The failures in intelligence-sharing were attributed to 1995 Justice Department policies limiting intelligence sharing, combined with CIA and NSA reluctance to reveal "sensitive sources and methods" such as tapped phones. 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". Clarke also wrote: " ere were... failures to get information to the right place at the right time."

Attacks

Early on the morning of September 11, 2001, 19 hijackers took control of four commercial airliners (two Boeing 757s and two Boeing 767s) en route to California (three of them headed to LAX in Los Angeles and one to SFO in San Francisco) after takeoffs from Logan International Airport in Boston, Massachusetts; Newark Liberty International Airport in Newark, New Jersey; and Washington Dulles International Airport in Loudoun and Fairfax counties in Virginia. Large planes with long coast-to-coast flights were selected for hijacking because they would have more fuel.

The four flights were:
* American Airlines Flight 11: a Boeing 767 aircraft, departed Logan Airport at 7:59a.m. en route to Los Angeles with a crew of 11 and 76 passengers, not including five hijackers. The hijackers flew the plane into the northern façade of the North Tower of the World Trade Center in New York City at 8:46a.m.
* United Airlines Flight 175: a Boeing 767 aircraft, departed Logan Airport at 8:14a.m. en route to Los Angeles with a crew of nine and 51 passengers, not including five hijackers. The hijackers flew the plane into the southern façade of the South Tower of the World Trade Center in New York City at 9:03a.m.
* American Airlines Flight 77: a Boeing 757 aircraft, departed Washington Dulles International Airport at 8:20a.m. en route to Los Angeles with a crew of six and 53 passengers, not including five hijackers. The hijackers flew the plane into the western façade of the Pentagon in Arlington County, Virginia, at 9:37a.m.
* United Airlines Flight 93: a Boeing 757 aircraft, departed Newark International Airport at 8:42a.m. en route to San Francisco, with a crew of seven and 33 passengers, not including four hijackers. As passengers attempted to subdue the hijackers, the aircraft crashed into a field in Stonycreek Township, Pennsylvania, near Shanksville, at 10:03a.m.

Media coverage was extensive during the attacks and aftermath, beginning moments after the first crash into the World Trade Center.

* Eastern Daylight Time (UTC-04:00)
^† Excluding hijackers
^§ Including emergency workers
^‡ Including hijackers

The four crashes

At 7:59 a.m., American Airlines Flight 11 took off from Logan International Airport in Boston. Fifteen minutes into the flight, five hijackers armed with boxcutters took over the plane, injuring at least three people (and possibly killing one) before forcing their way into the cockpit. The terrorists also displayed an apparent explosive device in order to frighten the hostages into submission, while additionally spraying mace into the cabin to further hinder any efforts to resist. Back at Logan, United Airlines Flight 175 took off at 8:14 a.m., more or less the same time as Flight 11’s hijacking.Dulles International Airport in Fairfax and Loudoun Counties, Virginia, American Airlines Flight 77 left the runway at 8:20 a.m. Flight 175’s journey proceeded normally for 28 minutes until 8:42 a.m., when another group of five hijacked the plane, murdering both pilots and stabbing several crew members before assuming control of the aircraft. As was the case with Flight 11, the hijackers used bomb threats to instill fear into the passengers and crew and sprayed chemical weapons to disable any opposition. Concurrently, United Airlines Flight 93 departed from Newark International Airport in New Jersey; originally scheduled to pull away from the gate at 8:00 a.m., the plane was running 42 minutes late. At 8:46 a.m., Flight 11 was deliberately crashed into the north face of the World Trade Center's North Tower (1 WTC). At 8:51 a.m., shortly after the North Tower was struck and only minutes following the hijacking of Flight 175, American Airlines Flight 77 was also taken over by another group of five who forcibly entered the cockpit 31 minutes after takeoff. Although the hijackers were equipped with knives that they threatened their victims with, there were no reports of anyone on board actually being stabbed unlike the first two planes, nor did the two people who made phone calls mention the use of mace or a bomb threat of any kind. At 9:03 a.m., seventeen minutes after the first plane crashed into the North Tower, Flight 175 was flown into the South Tower's southern facade (2WTC). After waiting 46 minutes to make their move—a holdup which proved disastrous for the terrorists when combined with the delayed takeoff from the runway—four men aboard Flight 93 struck suddenly, killing at least one passenger before storming the cockpit and seizing control of the plane at 9:28 a.m., turning the plane east and setting course for Washington D.C. Much like their counterparts on the first two flights, the fourth team also used bomb threats to get their way and again filled the cabin with mace. Nine minutes after Flight 93's hijacking, Flight 77 was crashed into the Pentagon. Because of the two delays, the passengers and crew of Flight 93 had time to be made aware of the previous attacks through phone calls to the ground. Knowing their lives were forfeited rendered the bomb threat moot, and an uprising was hastily organized in the hopes of gaining control of the aircraft, with an assault on the hijackers being launched at 9:57 a.m. Within minutes, they had fought their way to the front of the cabin and began breaking down the cockpit door. Fearing their captives would gain the upper hand, the hijackers rolled the plane and pitched it into a nosedive, crashing it into a field near Shanksville, Pennsylvania, southeast of Pittsburgh, at 10:03 a.m. The plane was around 20 minutes away from reaching D.C. at the time of the crash, and its target is believed to have been either the Capitol Building or the White House.

Some passengers and crew members who called from the aircraft using the cabin air phone service and mobile phones provided details: several hijackers were aboard each plane; they used mace, tear gas, or pepper spray to overcome attendants; and some people aboard had been stabbed.*
*
* Summers and Swan (2011), pp. 58, 463n, 476n.
*
*
*
* Reports indicated hijackers stabbed and killed pilots, flight attendants, and one or more passengers.9/11 Commission Report, pp. 4–14. According to the 9/11 Commission's final report, the hijackers had recently purchased multi-function hand tools and assorted Leatherman-type utility knives with locking blades (which were not forbidden to passengers at the time), but were not found among the possessions left behind by the hijackers. A flight attendant on Flight 11, a passenger on Flight 175, and passengers on Flight 93 said the hijackers had bombs, but one of the passengers said he thought the bombs were fake. The FBI found no traces of explosives at the crash sites, and the 9/11 Commission concluded that the bombs were probably fake. On at least two of the hijacked flights―American 11 and United 93―the terrorists tried to ensure nobody would resist by claiming over the PA system that they were taking hostages and were returning to the airport to have a ransom demand met, an obvious attempt to deceive those on-board into staying put by way of a false hope. Both of these attempts fell on deaf ears, however, as the hijacker pilots in both instances (Mohamed Atta and Ziad Jarrah, respectively) keyed the wrong switch and mistakenly transmitted their messages to ATC instead of the people on the plane as intended, in the process tipping off the flight controllers that the planes had been hijacked.

Three buildings in the World Trade Center collapsed due to fire-induced structural failure. The South Tower collapsed at 9:58a.m., having burned for 55minutes in a fire caused by the impact of United Airlines Flight 175 and the explosion of its fuel. The North Tower collapsed at 10:28 a.m. after burning for 102 minutes. When the North Tower collapsed, debris fell on the nearby 7 World Trade Center building (7WTC), damaging the building and starting fires. These fires burned for nearly seven hours, compromising the building's structural integrity, and 7WTC collapsed at 5:21p.m. The west side of the Pentagon sustained significant damage.

At 9:42 a.m., the Federal Aviation Administration (FAA) grounded all civilian aircraft within the continental U.S., and civilian aircraft already in flight were told to land immediately. All international civilian aircraft were either turned back or redirected to airports in Canada or Mexico, and were banned from landing on United States territory for three days. The attacks created widespread confusion among news organizations and air traffic controllers. Among the unconfirmed and often contradictory news reports aired throughout the day, one of the most prevalent said a car bomb had been detonated at the U.S. State Department's headquarters in Washington, D.C. Another jet (Delta Air Lines Flight 1989) was suspected of having been hijacked, but the aircraft responded to controllers and landed safely in Cleveland, Ohio.

In an April 2002 interview, Khalid Sheikh Mohammed and Ramzi bin al-Shibh, who are believed to have organized the attacks, said Flight 93's intended target was the United States Capitol, not the White House. During the planning stage of the attacks, Mohamed Atta (Flight 11's hijacker and pilot) thought the White House might be too tough a target and sought an assessment from Hani Hanjour (who hijacked and piloted Flight 77).Summers and Swan (2011), p. 323. Mohammed said al-Qaeda initially planned to target nuclear installations rather than the World Trade Center and the Pentagon, but decided against it, fearing things could "get out of control". Final decisions on targets, according to Mohammed, were left in the hands of the pilots. If any pilot could not reach his intended target, he was to crash the plane.

Casualties

The attacks are the deadliest terrorist attacks in world history, causing the deaths of 2,996 people (including the hijackers) and injuring thousands of others. The death toll included 265 on the four planes (from which there were no survivors); 2,606 in the World Trade Center and in the surrounding area; and 125 at the Pentagon. Most who died were civilians; the rest included 343 firefighters, 72 law enforcement officers, 55 military personnel, and the 19 terrorists. After New York, New Jersey lost the most state citizens. More than 90 countries lost citizens in the attacks; for example, the 67 Britons who died were more than in any other terrorist attack anywhere.

In Arlington County, Virginia, 125 Pentagon workers died when Flight 77 crashed into the building's western side. Seventy were civilians and 55 were military personnel, many of whom worked for the United States Army or the United States Navy. The Army lost 47 civilian employees; six civilian contractors; and 22 soldiers, while the Navy lost six civilian employees; three civilian contractors; and 33 sailors. Seven Defense Intelligence Agency (DIA) civilian employees died, and one Office of the Secretary of Defense (OSD) contractor. Lieutenant General Timothy Maude, an Army Deputy Chief of Staff, was the highest-ranking military official killed at the Pentagon.

In New York City, more than 90% of the workers and visitors who died in the towers had been at or above the points of impact. In the North Tower, between 1,344 and 1,402 people were at, above or one floor below the point of impact and all died. Hundreds were killed instantly the moment the plane struck. The estimated 800 people who survived the impact were trapped and died in the fires or from smoke inhalation; fell or jumped from the tower to escape the smoke and flames; or were killed in the building's collapse. The destruction of all three staircases in the tower when Flight 11 hit made it impossible for anyone from the impact zone upwards to escape. 107 people below the point of impact died, including every single occupant of Floor 92, which was right underneath the plane's impact zone.

In the South Tower, around 600 people were on or above the 77th floor with Flight 175 crashed into the building. As with the North Tower, hundreds were killed at the moment of impact. The estimated 300 people above the impact zone who survived the crash were unware that, unlike in the North Tower, escape was still possible. One stairway, Stairwell A, was left intact after Flight 175 hit, allowing 14 people located on the floors of impact (including Stanley Praimnath, a man who saw the plane coming at him) and four more from the floors above to escape. New York City 9-1-1 operators who received calls from people inside the tower were not well informed of the situation as it rapidly unfolded and as a result, told callers not to descend the tower on their own. In total 630 people died in the South Tower, fewer than half the number killed in the North Tower. In stark contrast to the North Tower, where nearly 200 people fell to their deaths from above the impact zone, only three people were spotted jumping or falling from the upper floors of the South Tower. Casualties in the South Tower were significantly reduced because some occupants decided to leave the building as soon as the North Tower was struck, and because Rick Rescorla, head of security at Morgan Stanley, defied an order to remain in place and evacuated almost all of the company's 2,700 employees in the South Tower to safety after Flight 11 had struck the North Tower. Eric Eisenberg, an executive at AON Insurance, similarly made the decision to evacuate the floors occupied by AON in the moments following the impact of Flight 11, although the company still lost 175 employees in the South Tower. Other pre-impact evacuations were carried out companies such as Fiduciary Trust, CSC, and Euro Brokers―all of whom had offices on floors above the point of impact. The failure to order a full evacuation of the South Tower after the first jet crash into the North Tower was described by '' USA Today'' as "one of the day's great tragedies".

At least 200 people fell or jumped to their deaths from the burning towers (as exemplified in the photograph '' The Falling Man''), landing on the streets and rooftops of adjacent buildings hundreds of feet below. Some occupants of each tower above the point of impact made their way toward the roof in the hope of helicopter rescue, but the roof access doors were locked. No plan existed for helicopter rescues, and the combination of roof equipment, thick smoke, and intense heat prevented helicopters from approaching.

A total of 411 emergency workers died as they tried to rescue people and fight fires. The New York City Fire Department (FDNY) lost 343 firefighters, including a chaplain and two paramedics. The New York City Police Department (NYPD) lost 23 officers. The Port Authority Police Department (PAPD) lost 37 officers. Eight emergency medical technicians (EMTs) and paramedics from private emergency medical services (EMS) units were killed.

Cantor Fitzgerald L.P. (an investment bank on the North Tower's 101st–105th floors) lost 658 employees, considerably more than any other employer. Marsh Inc., located immediately below Cantor Fitzgerald on floors 93–100, lost 358 employees, and 175 employees of Aon Corporation were also killed. The National Institute of Standards and Technology (NIST) estimated that about 17,400 civilians were in the World Trade Center complex at the time of the attacks. Turnstile counts from the Port Authority suggest 14,154 people were typically in the Twin Towers by 8:45a.m. Most people below the impact zone safely evacuated the buildings.

Weeks after the attack, the death toll was estimated to be over 6,000, more than twice the number of deaths eventually confirmed. The city was only able to identify remains for about 1,600 of the World Trade Center victims. The medical examiner's office collected "about 10,000 unidentified bone and tissue fragments that cannot be matched to the list of the dead". Bone fragments were still being found in 2006 by workers who were preparing to demolish the damaged Deutsche Bank Building.

In 2010, a team of anthropologists and archaeologists searched for human remains and personal items at the Fresh Kills Landfill, where 72 more human remains were recovered, bringing the total found to 1,845. DNA profiling continues in an attempt to identify additional victims. The remains are being held in storage in Memorial Park, outside the New York City Medical Examiner's facilities. It was expected that the remains would be moved in 2013 to a repository behind a wall at the 9/11 museum.

In July 2011, a team of scientists at the Office of Chief Medical Examiner was still trying to identify remains, in the hope that improved technology will allow them to identify other victims. On August 7, 2017, the 1,641st victim was identified as a result of newly available DNA technology, and a 1,642nd on July 26, 2018. Three more victims were identified in 2019 and further two in 2021. As of September 2021, 1,106 victims are yet to be identified.

Damage

Along with the 110-floor Twin Towers, numerous other buildings at the World Trade Center site were destroyed or badly damaged, including WTC buildings 3through7 and St. Nicholas Greek Orthodox Church. The North Tower, South Tower, the Marriott Hotel (3WTC), and 7WTC were destroyed. The U.S. Customs House ( 6 World Trade Center), 4World Trade Center, 5 World Trade Center, and both pedestrian bridges connecting buildings were severely damaged. The Deutsche Bank Building (still popularly referred to as the Bankers Trust Building) on 130 Liberty Street was partially damaged and demolished some years later, starting in 2007.Summers and Swan (2011), p. 75. The two buildings of the World Financial Center also suffered damage. The last fires at the World Trade Center site were extinguished on December 20, exactly 100 days after the attacks.

The Deutsche Bank Building across Liberty Street from the World Trade Center complex was later condemned as uninhabitable because of toxic conditions inside the office tower, and was deconstructed. The Borough of Manhattan Community College's Fiterman Hall at 30 West Broadway was condemned due to extensive damage from the attacks, and was reopened in 2012.

Other neighboring buildings (including 90 West Street and the Verizon Building) suffered major damage but have been restored. World Financial Center buildings, One Liberty Plaza, the Millenium Hilton, and 90 Church Street had moderate damage and have since been restored. Communications equipment on top of the North Tower was also destroyed, with only WCBS-TV maintaining a backup transmitter on the Empire State Building, but media stations were quickly able to reroute the signals and resume their broadcasts.

The PATH train system's World Trade Center station was located under the complex. As a result, the entire station was demolished completely when the towers collapsed, and the tunnels leading to Exchange Place station in Jersey City, New Jersey