September 11 attacks

al-Qaeda

Company type	Militant Islamist organization
Industry	Terrorism
Founded	1988
Founder	Osama bin Laden
Area served	Global
Key people	Osama bin Laden, Khalid Sheikh Mohammed, Ayman al-Zawahiri

September 11 Attacks Overview

The September 11 attacks, frequently referred to as 9/11, involved a series of four synchronized suicide terrorist strikes orchestrated by al-Qaeda against the United States in 2001. A group of nineteen militants commandeered four commercial airplanes, directing two into the Twin Towers of the World Trade Center located in New York City, and a third into the Pentagon in Arlington County, Virginia. The fourth hijacked aircraft crashed into a rural area in Pennsylvania after passengers attempted to regain control. These attacks resulted in 2,977 fatalities, constituting the deadliest act of terrorism ever recorded and initiating the global war on terror.

Leading the operation, Mohamed Atta piloted American Airlines Flight 11, which struck the North Tower at around 8:46 a.m. Shortly thereafter, at approximately 9:03 a.m., United Airlines Flight 175 collided with the South Tower. Both towers collapsed within one hour and forty-two minutes, causing the destruction of five additional buildings within the complex. At 9:37 a.m., American Airlines Flight 77 impacted the Pentagon, resulting in partial structural collapse. The final hijacked plane, United Airlines Flight 93, intended to target either the United States Capitol or the White House, but crashed near Shanksville, Pennsylvania at 10:03 a.m. following resistance from passengers. In response, the Federal Aviation Administration halted all U.S. air traffic indefinitely, while Canada implemented Operation Yellow Ribbon to manage diverted flights.

That same evening, the Central Intelligence Agency attributed responsibility to al-Qaeda and its leader, Osama bin Laden. This led to the initiation of the war on terror by the U.S., including military intervention in Afghanistan aimed at toppling the Taliban regime for providing sanctuary to al-Qaeda operatives. For the first time ever, NATO invoked Article 5, committing allied nations to combat al-Qaeda on a global scale. Bin Laden initially denied involvement but publicly claimed responsibility in 2004. Al-Qaeda cited motivations such as U.S. backing of Israel, military bases stationed in Saudi Arabia, and sanctions imposed on Iraq. The extensive pursuit of bin Laden concluded with his death during a U.S. special forces operation in Pakistan in 2011. The conflict in Afghanistan persisted until a withdrawal agreement was finalized in 2020.

The attacks caused nearly 3,000 deaths and thousands more injuries, inflicted infrastructure damage exceeding billions of dollars, and led to enduring health issues among first responders and survivors. It stands as the deadliest terrorist incident and greatest loss of firefighters and law enforcement personnel in American history. The devastation deeply affected the U.S. economy and triggered worldwide financial turmoil, prompting numerous nations to enhance their counterterrorism legislation and expand intelligence operations. Combined casualties from ensuing conflicts linked to these events are estimated to surpass 4.5 million.

Cleanup efforts at the World Trade Center site—known as "Ground Zero"—were completed by May 2002; repairs at the Pentagon were finalized within one year. Reconstruction plans encompassed six new buildings along with memorials and a museum dedicated to honoring victims and emergency personnel. Construction on One World Trade Center commenced in 2006 and was completed by 2014. Memorial sites include the National September 11 Memorial & Museum in New York City, the Pentagon Memorial in Arlington County, Virginia, and the Flight 93 National Memorial located at the Pennsylvania crash location.

Background

In 1996, Osama bin Laden, leader of the Islamist militant organization al-Qaeda, issued his initial fatwā, declaring a campaign against the United States and calling for the withdrawal of all American forces from the Arabian Peninsula. A subsequent fatwā in 1998 condemned U.S. foreign policy concerning Israel and criticized the ongoing American military presence in Saudi Arabia following the Gulf War. Bin Laden asserted that Muslims were compelled to target American interests until U.S. actions perceived as hostile to Muslims were reversed.

The Hamburg cell in Germany consisted of prominent al-Qaeda operatives who played central roles in the 9/11 attacks: Mohamed Atta, Marwan al-Shehhi, Ziad Jarrah, Ramzi bin al-Shibh, and Said Bahaji. Bin Laden portrayed these operations as acts of self-defense aimed at pressuring the United States to reconsider its backing of Israel and other aggressive policies.

In a 1998 interview with journalist John Miller, bin Laden stated:

Osama bin Laden

Bin Laden was the mastermind behind the September 11 attacks. Although he initially denied any involvement, he later accepted responsibility. On September 16, 2001, Al Jazeera broadcast a statement in which he refuted participation; however, by November 2001, U.S. forces had obtained a videotape where he acknowledged prior knowledge of the attacks.

In a video released on December 27, 2001, bin Laden stopped short of fully admitting direct responsibility but lauded terrorist acts against America as justified retaliation for perceived injustices. He emphasized targeting the U.S. economy as a means to undermine its military capabilities.

Prior to the 2004 U.S. presidential election, bin Laden openly confirmed al-Qaeda’s role in orchestrating the attacks, citing American support for Israel and previous conflicts as motivating factors. He explained that demolishing the towers was intended as retribution for violence inflicted upon Muslims and as a deterrent against further assaults on women and children. Bin Laden personally oversaw the planning of attacks on both the World Trade Center and the Pentagon.

In a 2006 video obtained by Al Jazeera, bin Laden appeared alongside key planners and hijackers involved in preparing for the attacks.

Khalid Sheikh Mohammed and other al-Qaeda members

According to Al Jazeera journalist Yosri Fouda, in April 2002 al-Qaeda operative Khalid Sheikh Mohammed confessed to participating in the attacks with Ramzi bin al-Shibh. The 2004 9/11 Commission Report identified Mohammed as the chief architect behind the September 11 operation, driven by opposition to U.S. policies favoring Israel. He also served as an advisor and financier for the 1993 World Trade Center bombing and was uncle to Ramzi Yousef, who led that attack.

In late 1994, Mohammed and Yousef devised the Bojinka plot—a terrorist scheme planned for January 1995—that influenced later aspects of the 9/11 attacks despite Yousef's capture.

During Zacarias Moussaoui’s trial, five individuals were named as fully informed about the operation’s specifics: Osama bin Laden, Khalid Sheikh Mohammed, Ramzi bin al-Shibh, Abu Turab al-Urduni, and Mohammed Atef.

Motives

Osama bin Laden's proclamation of a jihad against the United States, including his 1998 fatwā calling for the killing of Americans, serves as pivotal evidence of his underlying motives. In a November 2001 statement, bin Laden portrayed the attacks as vengeance for U.S. actions against Muslims worldwide, stressing that the selected targets represented America's "economic and military strength" rather than ordinary civilians.

In his November 2002 Letter to the American People, bin Laden detailed al-Qaeda's grievances:

• U.S. backing of Israel and its support for the Second Intifada
• Military interventions by a U.S.-led coalition against Muslims in Somalia
• American endorsement of regimes opposing Muslim interests in regions such as the Philippines, Lebanon, Chechnya, and Kashmir
• Deployment of U.S. forces on Saudi soil
• Imposition of sanctions on Iraq
• Environmental harm attributed to U.S. policies

After the attacks, both bin Laden and Ayman al-Zawahiri issued recordings reaffirming these justifications. Bin Laden claimed the assaults targeted military and financial institutions exclusively, aligning with his belief that non-Muslim military presence in the Arabian Peninsula was prohibited. His 1996 fatwā demanded removal of U.S. troops from Saudi Arabia; experts believe this stance was instrumental in recruiting suicide attackers.

Bin Laden also linked the concept of striking the World Trade Center to his observations of Israel’s bombardment during the 1982 Lebanon War. Analysts frequently point to U.S. support for Israel as a major catalyst behind the attacks. Later communications from bin Laden indicated plans to continue assaults as long as American support for Israel remained, aiming to "destroy and bankrupt" the United States.

Further interpretations suggest motivations such as perceived humiliation due to the Islamic world’s lag behind Western powers amid globalization and a calculated attempt to ignite a wider conflict to spark a pan-Islamic uprising. Some analysts contend bin Laden intended to provoke widespread Muslim resistance by eliciting U.S. military retaliation, thereby unifying Islamist factions against Western influence and promoting conservative Islamic governance throughout the Middle East.

Planning

Among documents recovered during the 2011 operation that killed bin Laden were handwritten notes by bin Laden dated September 2002 entitled "The Birth of the Idea of September 11". He referenced inspiration drawn from the intentional crash of EgyptAir Flight 990 in October 1999, which resulted in over 200 fatalities. Bin Laden indicated that only Mohammed Atef and Abu al-Khair were initially aware of this plan. The 9/11 Commission Report identified Khalid Sheikh Mohammed as the mastermind behind the plot, although he does not appear in bin Laden’s notes.

The proposal for the attacks was first presented to bin Laden by Khalid Sheikh Mohammed in 1996, coinciding with al-Qaeda’s relocation back to Afghanistan from Sudan. The 1998 bombings of African embassies alongside bin Laden’s February 1998 fatwā marked a strategic pivot towards targeting U.S. interests.

By late 1998 or early 1999, bin Laden had authorized Mohammed to coordinate the operation. Mohammed Atef provided logistical support including selecting targets and facilitating travel arrangements for hijackers. Bin Laden vetoed certain proposed targets such as the U.S. Bank Tower in Los Angeles due to time limitations.

Bin Laden personally managed financing, recruitment, and overall command. He initially selected seasoned jihadists Nawaf al-Hazmi and Khalid al-Mihdhar, who arrived in the United States in January 2000 and undertook flight training in San Diego before acting as secondary hijackers.

In late 1999, recruits from Hamburg, Germany—Mohamed Atta, Marwan al-Shehhi, Ziad Jarrah, and Ramzi bin al-Shibh—joined al-Qaeda in Afghanistan. Bin Laden preferred them due to their education level, English proficiency, and familiarity with Western culture. Among these recruits was Hani Hanjour, a certified commercial pilot who arrived in San Diego in December 2000 and completed refresher training in Arizona.

Marwan al-Shehhi entered the U.S. in May 2000; Atta and Jarrah followed in June. Bin al-Shibh repeatedly failed to secure a U.S. visa amid concerns about overstaying and stayed in Hamburg to coordinate with Atta and Mohammed. These three Hamburg cell members received pilot training at Huffman Aviation in South Florida.

Secondary hijackers entered the United States during spring 2001. In July that year, Atta met with bin al-Shibh in Tarragona, Spain, where they finalized operational details and target selection; bin al-Shibh conveyed bin Laden’s insistence on rapid execution. Some hijackers acquired passports through corrupt Saudi officials or used forged documents to gain entry into the U.S.

Prior intelligence

Toward the end of 1999, al-Qaeda operative Walid bin Attash (known as "Khallad") reached out to Mihdhar to arrange a meeting in Kuala Lumpur, Malaysia, which was also attended by Hazmi and Abu Bara al Yemeni. The NSA intercepted a communication referencing this gathering along with the names Mihdhar and "Nawaf" (Hazmi), but no subsequent measures were taken.

Saudi intelligence had alerted the CIA regarding Mihdhar and Hazmi’s connections to al-Qaeda. A CIA team conducted a search of Mihdhar's hotel room in Dubai and discovered he possessed a U.S. visa. Although this intelligence was shared with international agencies, the FBI was not informed. The Malaysian Special Branch monitored the January 5, 2000 meeting and notified the CIA that Mihdhar, Hazmi, and Khallad were traveling to Bangkok. However, this intelligence was neither disseminated to other agencies nor used to add Mihdhar to any watchlists. When an FBI liaison requested notification of such developments, the response was that it was "not a matter for the FBI."

By late June 2001, senior officials in counter-terrorism, including Richard A. Clarke and CIA director George Tenet, anticipated a significant attack but expected it to occur in Saudi Arabia or Israel. In early July, Clarke placed domestic agencies on "full alert," urging enhanced coordination among the FBI, State Department, and Defense Department. Clarke later remarked that despite receiving intelligence about terrorists and suspicious activities at U.S. flight schools, critical information failed to reach him or the White House.

Within al-Qaeda's leadership, disagreements arose over when to launch attacks against the U.S., with bin Laden advocating for immediate operations to support the Second Intifada and oppose U.S. military presence in Saudi Arabia.

On July 13, CIA officer Tom Wilshire sought authorization to inform the FBI that Hazmi was present in the U.S. and that Mihdhar held a visa; however, no reply was given by the CIA. On that same day, FBI analyst Margarette Gillespie reviewed documents concerning the Malaysia meeting but remained unaware of Hazmi’s and Mihdhar’s presence in the United States. Surveillance photographs were distributed without essential context or details, limiting FBI counterterrorism capabilities. By late August 2001, Gillespie recommended that several agencies add Hazmi and Mihdhar to watchlists; nevertheless, FBI limitations on involving criminal investigators hindered search efforts.

Also during July, Phoenix FBI agent Kenneth Williams raised concerns about a possible coordinated initiative by bin Laden involving sending students to U.S. flight schools. He suggested interviewing flight school administrators and identifying Arab individuals seeking pilot training. Jordan warned U.S. authorities about an imminent al-Qaeda operation dubbed "The Big Wedding," involving aircraft.

The CIA’s Presidential Daily Brief dated August 6, 2001, titled Bin Ladin Determined To Strike in US, emphasized FBI reports describing suspicious behavior consistent with hijacking preparations.

In mid-August, a flight school in Minnesota reported Zacarias Moussaoui’s unusual conduct to the FBI. Despite identifying Moussaoui as a radical and detaining him for visa overstay, FBI headquarters denied requests for laptop searches due to insufficient probable cause.

Failures in intelligence sharing originated from Justice Department policies established in 1995 that restricted cooperation between criminal investigators and intelligence personnel. These issues were exacerbated by CIA and NSA hesitance to disclose sensitive sources. Then-Attorney General John Ashcroft testified that this "wall" represented a significant structural barrier contributing to intelligence shortcomings before September 11. Clarke also pointed out that delays in sharing information were critical failures contributing to these gaps.

Attacks

In the early hours of September 11, 2001, nineteen terrorists took control of four commercial aircraft—comprising two Boeing 757s and two Boeing 767s. The hijackers specifically targeted large, long-haul jets because of their substantial fuel capacity.

Essential details regarding the four flights

Airline	Flight number	Aircraft model	Departure time*	Crash time*	Origin airport	Destination airport	Impact location	Casualties
								Crew	Passengers†	Ground§	Hijackers	Total‡
American Airlines	11	Boeing 767-223(ER)	7:59 a.m.	8:46 a.m.	Logan International Airport	Los Angeles International Airport	North Tower of the World Trade Center, floors 93 through 99	11	76	2,606	5	2,763
United Airlines	175	Boeing 767–222	8:14 a.m.	9:03 a.m.	Logan International Airport	Los Angeles International Airport	South Tower of the World Trade Center, floors 77 through 85	9	51		5
American Airlines	77	Boeing 757–223	8:20 a.m.	9:37 a.m.	Washington Dulles International Airport	Los Angeles International Airport	West side of The Pentagon	6	53	125	5	189
United Airlines	93	Boeing 757–222	8:42 a.m.	10:03 a.m.	Newark International Airport	San Francisco International Airport	Field in Stonycreek Township, Somerset County, Pennsylvania near Shanksville	7	33	0	4	44

* Times are given in Eastern Daylight Time
^† Does not include hijackers
^§ Includes emergency responders
^‡ Includes hijackers

Crashes

At 7:59 a.m., American Airlines Flight 11 departed from Boston’s Logan International Airport. Approximately fifteen minutes into the journey, five hijackers equipped with boxcutters seized control, injuring several passengers before forcing entry into the cockpit. They reportedly used an explosive device and deployed mace to intimidate those on board. Shortly thereafter, United Airlines Flight 175 took off at 8:14 a.m., followed by American Airlines Flight 77 departing from Dulles International Airport at 8:20 a.m. Flight 175 was overtaken 28 minutes into its flight; the hijackers killed both pilots and employed bomb threats along with irritants to subdue passengers. Meanwhile, United Airlines Flight 93 departed Newark International Airport after a 42-minute delay.

At 8:46 a.m., Flight 11 crashed into the north side of the World Trade Center’s North Tower, striking between floors 93 and 99. Initially regarded as an accident, it was soon confirmed to be a deliberate attack. At 8:51 a.m., Flight 77 was hijacked post-takeoff. Although knives were used during the takeover, no stabbings were reported onboard. At 9:03 a.m., Flight 175 impacted the South Tower between floors 77 and 85, confirming the attacks were acts of terrorism.

Flight 93 was hijacked at 9:28 a.m., with terrorists redirecting it toward Washington, D.C. Nine minutes later, at 9:37 a.m., Flight 77 crashed into the Pentagon’s west side. Due to prior delays, passengers on Flight 93 became aware of earlier attacks through phone communications and coordinated a counterattack at 9:57 a.m., managing to breach the cockpit door. Subsequently, hijackers deliberately crashed the plane near Shanksville, Pennsylvania, at 10:03 a.m., presumably aiming for either the Capitol or White House.

Information relayed by passengers and crew via phone calls indicated multiple hijackers per aircraft, use of mace or similar irritants to incapacitate flight attendants, and some stabbing incidents. Although utility knives were present among hijackers, no explosives were discovered; bomb threats appeared to be deceptive tactics. On Flights 11 and 93, hijackers falsely claimed hostage situations and ransom demands to discourage resistance; however, these ploys failed as pilots inadvertently transmitted messages to air traffic control.

Three World Trade Center structures collapsed due to fire-induced structural failure. The South Tower was the first to fall at 9:59 a.m., after burning for approximately 56 minutes following Flight 175’s impact. The North Tower collapsed at 10:28 a.m., roughly one hour and forty-two minutes after being struck by Flight 11. Debris from this collapse damaged nearby 7 World Trade Center, which burned for nearly seven hours before collapsing at 5:21 p.m. The Pentagon suffered extensive damage on its western facade.

At 9:42 a.m., the Federal Aviation Administration issued a ground stop for all civilian flights within the continental United States; international flights were either redirected or returned for three days following the attacks. These events caused significant confusion among news outlets and air traffic controllers, resulting in erroneous reports such as a car bomb at the State Department and suspected hijackings of other flights that ultimately landed safely.

In an interview conducted in April 2002, Khalid Sheikh Mohammed and Ramzi bin al-Shibh confirmed that Flight 93’s intended target was the U.S. Capitol rather than the White House. Early al-Qaeda plans had considered nuclear targets but shifted focus toward the World Trade Center and Pentagon due to concerns over uncontrollable outcomes. Final decisions regarding targets were delegated to pilots; if unable to reach their assigned targets, they were instructed to crash their aircraft deliberately.

Casualties

The assault on the North Tower of the World Trade Center rendered 9/11 the most lethal terrorist incident ever recorded. The four hijacked flights resulted in a total of 2,996 fatalities (including the attackers) and caused injuries to thousands more. The fatalities comprised 265 individuals aboard the planes; 2,606 within and around the World Trade Center; and 125 at the Pentagon. The majority of those killed were civilians, accompanied by 343 firefighters, 72 law enforcement officers, 55 military members, and 19 terrorists. Citizens from over 90 nations lost their lives in these attacks.

In New York City, more than 90% of casualties in the towers occurred at or above the impact zones. The North Tower saw between 1,344 and 1,402 people perish instantly or succumb to fires and structural collapse near the crash site. Escape was rendered impossible for occupants above the impact as all stairwells were destroyed. In the South Tower, approximately 600 people were located on or above the 77th floor when it was struck; fewer than half survived. However, one stairwell remained usable, allowing some to evacuate. Proactive evacuations initiated by companies such as AON Insurance notably decreased fatalities in this tower.

Over 200 individuals died after falling from the towers, many forced to jump to avoid smoke and flames. Attempts to rescue occupants via rooftop helicopters were unsuccessful due to locked access points and dangerous conditions.

Within the World Trade Center complex, rescue operations claimed the lives of 414 emergency responders: this included 343 firefighters (among them chaplains and paramedics), 23 New York Police Department officers, and 37 Port Authority Police officers. Additionally, eight EMTs and paramedics from private ambulance services lost their lives. The majority of these emergency personnel perished during the collapse of the buildings.

Several major employers experienced significant losses: Cantor Fitzgerald lost 658 staff members; Marsh Inc., 358; and Aon Corporation, 175. Around 17,400 civilians were inside the complex at the time of attack; most situated below the impact areas managed to evacuate safely.

At the Pentagon, Flight 77’s impact resulted in 125 deaths among workers—70 civilians and 55 military personnel—including Lieutenant General Timothy Maude, Army Deputy Chief of Staff and highest-ranking military fatality.

Early estimates of fatalities exceeded 6,000 but were later adjusted to confirmed numbers. Positive identification was made for roughly 1,600 victims from the World Trade Center; thousands of bone fragments remain unidentified. Remains continued to be discovered for years during ongoing site clearance efforts.

By 2011, DNA analysis remained active in identifying additional victims. In 2014, nearly 8,000 unidentified remains were relocated to a repository near the National September 11 Memorial & Museum—a move that has been met with criticism from some families seeking above-ground burial.

Technological advances in DNA profiling have enabled new identifications long after the attacks: as of 2025, over 1,600 victims have been identified posthumously; however, about 1,103 remain unidentified—accounting for approximately 40% of World Trade Center fatalities. In September 2023, FDNY announced that deaths among its members due to illnesses related to 9/11 now equal those who died on that day itself.

Damage

The Twin Towers, along with the Marriott World Trade Center (3WTC), 7WTC, and the St. Nicholas Greek Orthodox Church, were completely destroyed. Severe damage was inflicted on the U.S. Customs House (6 World Trade Center), 4 World Trade Center, 5 World Trade Center, as well as the pedestrian bridges. The surrounding streets were left devastated. The final fires at the site were extinguished by December 20, 2001.

The Deutsche Bank Building sustained significant damage and was later condemned due to hazardous conditions; its demolition commenced in 2007. Structures within the World Financial Center complex also suffered damage. The Borough of Manhattan Community College’s Fiterman Hall was condemned but reopened in 2012 following extensive repairs.

Nearby buildings such as 90 West Street and the Verizon Building incurred major damage but have since been restored. Other properties including the World Financial Center buildings, One Liberty Plaza, the Millennium Hilton, and 90 Church Street experienced moderate harm and have undergone repairs. Communications equipment located atop the North Tower was destroyed; nonetheless, media outlets rapidly rerouted transmissions and resumed broadcasting.

The PATH train line’s World Trade Center station, situated beneath the complex, was demolished during the towers' collapse, causing flooding in tunnels leading to Exchange Place station in Jersey City. This station was reconstructed as the $4 billion World Trade Center Transportation Hub, reopening in March 2015. The adjacent Cortlandt Street station on the New York City Subway’s IRT Broadway–Seventh Avenue Line was destroyed but later reopened on September 8, 2018.

The Pentagon endured extensive structural damage with a portion collapsing. As Flight 77 approached, its wings struck light poles and its right engine collided with a power generator before crashing into the western façade at ground-floor level. The front section of the fuselage disintegrated upon impact, while debris from the tail penetrated approximately through three of the building’s outermost rings.

Rescue efforts

The New York City Fire Department (FDNY) mobilized over 200 units—approximately half of its personnel—to respond at the World Trade Center site, supported by off-duty firefighters and emergency medical technicians. The New York City Police Department (NYPD) deployed Emergency Service Units, additional officers, and its aviation unit; however, helicopter rescues from the towers were deemed unfeasible. Officers from the Port Authority Police Department (PAPD) also took part in rescue operations. Coordination between FDNY, NYPD, and PAPD was limited, resulting in overlapping civilian search efforts.

As conditions deteriorated, evacuation orders were transmitted by the NYPD aviation unit; most NYPD officers evacuated prior to collapse. Communication was hampered by separate command centers and incompatible radio systems, which prevented FDNY commanders from receiving timely warnings. Following the collapse of the first tower, FDNY issued evacuation commands, but many firefighters did not receive them due to failures in radio repeater systems. Moreover, critical information from 9-1-1 callers failed to reach on-scene commanders despite being received by dispatchers.

Reactions

The assaults provoked swift reactions both domestically and internationally, encompassing governmental measures, closures, hate crime incidents, and military mobilizations. To provide compensation to victims and their families in return for relinquishing legal claims against the airlines involved, Congress created the September 11th Victim Compensation Fund. This fund was authorized to allocate up to $7.375 billion, including administrative expenses. Originally scheduled to expire in 2020, it was extended in 2019 to accept claims until 2090.

Immediate response

At 8:32 a.m., the FAA received notification that Flight 11 had been hijacked and promptly informed the North American Aerospace Defense Command (NORAD), which deployed two F-15 fighters from Otis Air National Guard Base by 8:53 a.m. Due to delayed FAA communication, NORAD was given only nine minutes’ warning and lacked information about other flights before their respective crashes.

Following the impact on both Twin Towers, additional fighter jets were launched from Joint Base Langley–Eustis at 9:30 a.m. At 10:20 a.m., Vice President Dick Cheney authorized shoot-down orders for hijacked commercial planes; however, this directive was not communicated in time. Some fighters took off without live ammunition but were prepared for extreme interception tactics.

For the first time ever, the Security Control of Air Traffic and Air Navigation Aids (SCATANA) emergency protocol was implemented, resulting in the grounding of tens of thousands of passengers globally. FAA National Operations Manager Ben Sliney ordered a complete closure of American airspace to incoming international flights, rerouting approximately 500 flights; Canada accepted 226 of these and initiated Operation Yellow Ribbon.

The attacks had an immediate societal impact. Police and emergency responders nationwide supported recovery operations in New York. More than 3,000 children lost one or both parents as a result. Blood donations across the United States surged significantly in the weeks that followed.

Domestic reactions

In the wake of the attacks, President Bush’s approval rating soared to 90%. On September 20, he addressed both the nation and a joint session of Congress, detailing ongoing rescue operations and his administration’s response plan. New York City Mayor Rudy Giuliani received widespread acclaim for his leadership during the crisis.

Multiple relief funds were established to offer financial support to survivors and families of victims. By the compensation claim deadline on September 11, 2003, a total of 2,833 applications had been filed by relatives of those who perished.

Contingency protocols for government continuity and evacuation plans for national leaders were immediately activated; however, Congress did not receive notification until February 2002.

Significant governmental restructuring followed with passage of the Homeland Security Act of 2002, which established the U.S. Department of Homeland Security. Additionally, Congress enacted the USA PATRIOT Act aimed at strengthening terrorism detection and prosecution efforts. Nonetheless, civil liberties advocates criticized this legislation for diminishing judicial oversight and infringing upon privacy rights.

The National Security Agency (NSA) was granted expanded authority to conduct warrantless surveillance of telecommunications. This program attracted criticism due to its allowance for eavesdropping on international communications without court warrants. The Foreign Intelligence Surveillance Court also approved broader governmental powers regarding collection and dissemination of information pertaining to both U.S. citizens and foreign nationals worldwide.

Hate crimes

Within a week following the attacks, President Bush visited the largest Islamic Center in Washington, D.C., recognizing the "incredibly valuable contribution" made by American Muslims and calling for respectful treatment toward them. In the days that followed, numerous reports emerged of harassment and hate crimes targeting Muslims and South Asian communities.

Sikhs also became victims due to their turbans being frequently mistaken for Muslim headwear. Incidents included assaults on mosques, religious sites—such as a Hindu temple that was firebombed—and individuals. One of the most notable cases was the fatal shooting of Balbir Singh Sodhi, a Sikh man killed in Mesa, Arizona, on September 15, 2001. Additionally, 24 relatives of Osama bin Laden were escorted out of the United States under FBI supervision just three days after the attacks.

Research indicated that individuals perceived as Middle Eastern were subjected to hate crimes at rates comparable to those targeting Muslims during this timeframe. The organization South Asian Americans Leading Together recorded 645 bias-related incidents against South Asians and Middle Eastern Americans from September 11 to 17, 2001. These incidents encompassed vandalism, arson, physical assaults, shootings, harassment, and threats occurring across various locations. Women wearing hijabs were frequently singled out as well.

Discrimination and racial profiling

A survey conducted in May 2002 revealed that one in five Arab-Americans had encountered discrimination since the events of September 11. Another poll carried out in July 2002 among Muslim Americans found that 48% felt their quality of life had declined post-9/11, with 57% reporting experiences of bias or discrimination. In response to such challenges, many Pakistani Americans began identifying themselves as Indians to avoid prejudice and improve job prospects.

By May 2002, the U.S. Equal Employment Opportunity Commission (EEOC) had received 488 complaints related to employment discrimination linked to the aftermath of the attacks; among these were 301 cases concerning wrongful terminations. Meanwhile, by June 2002, the U.S. Department of Transportation was investigating 111 complaints from airline passengers alleging religious or ethnic profiling during security checks, along with an additional 31 complaints regarding denied boarding for similar reasons.

Muslim American response

In the immediate aftermath, Muslim organizations across the United States swiftly condemned the attacks and encouraged Muslim Americans to offer their skills and resources to support those affected. Prominent groups involved included the Islamic Society of North America, American Muslim Alliance, American Muslim Council, Council on American-Islamic Relations, Islamic Circle of North America, and Shari'a Scholars Association of North America. Beyond financial contributions, these organizations coordinated blood donation drives and provided medical assistance, food supplies, and shelter for victims.

Interfaith efforts

Interest in Islam increased following the attacks, leading many mosques and Islamic centers to host open house events and outreach initiatives aimed at educating non-Muslim communities. Over the subsequent decade, participation in interfaith community service grew from 8% to 20%, while U.S. congregations engaging in interfaith worship doubled from 7% to 14%.

International reactions

The global response overwhelmingly condemned the attacks through media outlets and governmental statements, with numerous countries expressing solidarity with the United States. Most Middle Eastern governments—including Libya and Afghanistan—publicly denounced the attacks; Iraq notably issued a hostile statement opposing them. Saudi Arabia officially condemned the events as well, although some Saudis privately sympathized with bin Laden’s objectives.

Palestinian Authority President Yasser Arafat condemned the attacks; however, reports emerged about celebrations in Palestinian territories. Palestinian leaders disputed these accounts and maintained they did not represent public opinion. Later investigations disproved claims that footage showing celebrations was from earlier occasions. Worldwide tensions between Muslim and non-Muslim populations escalated after these events.

United Nations Security Council Resolution 1368 formally condemned the attacks and authorized counterterrorism actions under its Charter. Many nations enacted new anti-terror laws, froze assets linked to al-Qaeda suspects, and detained alleged terrorists.

British Prime Minister Tony Blair committed Britain’s full support by standing "shoulder to shoulder" with the United States. President Bush referred to Britain as America’s "truest friend," while Blair engaged in extensive diplomatic efforts to rally international backing for military intervention, holding 54 meetings with global leaders.

The U.S. established Guantanamo Bay detention camp for individuals designated as "illegal enemy combatants," a practice that drew criticism from both the European Union and human rights organizations.

On September 25, 2001, Iran’s President Mohammad Khatami expressed condolences toward the U.S., stressing that nations should not be penalized for acts committed by terrorists. Iranian citizens demonstrated mourning at Tehran’s Swiss Embassy—the representative office for U.S. interests there. Both Iran’s Supreme Leader and President condemned the attacks; vigils were documented by BBC and Time. Subsequently, Iran temporarily ceased its customary anti-American chants during Friday prayers following these events.

Military operations

At 2:40 p.m. on September 11, Secretary of Defense Donald Rumsfeld directed his aides to promptly gather intelligence on possible Iraqi involvement, instructing them to obtain the "best info fast" and to assess if the evidence justified targeting Saddam Hussein simultaneously, emphasizing that the focus should extend beyond Osama Bin Laden alone. During a meeting at Camp David on September 15, the Bush administration declined to launch an immediate strike against Iraq in retaliation for 9/11; however, in 2003, the U.S. and allied forces invaded Iraq, citing Saddam Hussein’s purported links to terrorism. At that time, surveys indicated that as many as 70% of Americans believed Saddam had a connection to the attacks, though President Bush later admitted three years afterward that this was not the case.

The NATO council invoked Article 5 of its charter for the first time since its establishment during the Cold War, declaring the 9/11 attacks an assault on all member states. Concurrently, Australian Prime Minister John Howard called upon Article IV of the ANZUS treaty. In response, the Bush administration initiated a comprehensive war on terror aimed at capturing bin Laden and dismantling al-Qaeda, while also preventing emerging terrorist groups by enforcing economic and military sanctions against nations sheltering terrorists and enhancing global intelligence cooperation and surveillance efforts.

On September 14, 2001, Congress enacted the Authorization for Use of Military Force Against Terrorists, empowering the President with broad authority to employ all necessary measures against those responsible for or harboring individuals involved in the attacks; this authorization remains active.

The conflict in Afghanistan commenced on October 7, 2001, with U.S. and British airstrikes targeting Taliban and al-Qaeda facilities, followed by Special Forces ground operations. These efforts culminated in the Taliban’s downfall marked by the capture of Kandahar on December 7 by coalition troops led by the United States.

Osama bin Laden evaded capture during the Battle of Tora Bora by retreating into Pakistan's border regions after hiding in Afghanistan’s White Mountains. He remained at large for nearly ten years. In an interview dated October 21, 2001, bin Laden condemned U.S. policies for prioritizing Israel’s interests over American security and portrayed America’s global approach as divisive. He argued that true security for the United States would only be achieved through withdrawal from the Arabian Peninsula and cessation of support for Israel.

Health issues

When the Twin Towers collapsed, hundreds of thousands of tons of hazardous debris containing more than 2,500 toxic substances and carcinogens were dispersed throughout Lower Manhattan. Exposure to these harmful materials contributed to serious and often fatal illnesses among first responders at Ground Zero as well as residents living nearby. Initially, under governmental guidance, the Environmental Protection Agency (EPA) assured the public about air safety but did not confirm that conditions had returned to pre-attack levels until June 2002.

The health consequences extended beyond responders to include local residents, students, and workers in Lower Manhattan and Chinatown. Numerous fatalities have been attributed to exposure to toxic dust, with victims honored at the World Trade Center memorial site. Approximately 18,000 individuals developed illnesses linked to dust exposure. Research has also indicated potential adverse effects on fetal development. A study conducted in 2010 revealed compromised lung function among all rescue personnel examined.

Legal battles over coverage of health-related expenses persisted years after the event. In 2006, a federal court permitted lawsuits against New York City concerning medical costs incurred by rescue workers. Officials faced scrutiny for promoting rapid returns to contaminated zones; EPA Administrator Christine Todd Whitman was notably criticized for prematurely declaring the area safe while Mayor Giuliani received backlash for urging financial sector employees to resume work on Wall Street without sufficient caution.

The James L. Zadroga 9/11 Health and Compensation Act passed in 2010 dedicated $4.2 billion to create the World Trade Center Health Program, which offers medical testing and treatment for chronic conditions associated with 9/11 exposure. This initiative replaced earlier programs such as the Medical Monitoring and Treatment Program.

By 2020, official records from the NYPD confirmed that 247 police officers had died due to illnesses related to their service following 9/11; by September 2022, FDNY reported 299 firefighter fatalities from similar causes. Both departments anticipate further increases in these numbers over time. The Port Authority Police Department (PAPD), responsible for security at the World Trade Center complex, reported four officer deaths linked to related illnesses. Unlike FDNY and NYPD—who rotated personnel through Ground Zero without adequate respiratory protection—PAPD leadership acted swiftly within two days by distributing industrial-grade respirators and restricting personnel exposure at the site, measures credited with reducing disease rates among their officers.

Economic

The attacks had a profound effect on both U.S. and international financial markets. Stock exchanges remained closed from September 11 to 17, reopening to witness the Dow Jones Industrial Average plunge by 684 points (7.1%)—marking its largest one-day point drop ever. By the end of that week, the DJIA had declined by 1,369.7 points (14.3%), erasing $1.4 trillion in market value.

In New York City, the aftermath resulted in the loss of approximately 430,000 job-months and $2.8 billion in wages during the first quarter, with export-related industries bearing the brunt. The city’s GDP decreased by $27.3 billion across late 2001 and all of 2002. To counteract these effects, the federal government disbursed $11.2 billion in immediate relief and an additional $10.5 billion early in 2002 aimed at economic revitalization and infrastructure improvements.

Small enterprises located near the World Trade Center faced severe consequences; roughly 18,000 businesses were either destroyed or displaced, leading to substantial employment and wage reductions. Support measures included loans from the Small Business Administration, Community Development Block Grants, and Economic Injury Disaster Loans. Damage or destruction affected around 31.9 million square feet of office space in Lower Manhattan, raising concerns about job recovery prospects and the stability of the local tax base. Nevertheless, the Manhattan office real estate sector and employment levels demonstrated greater resilience than anticipated, largely due to the financial services industry's reliance on direct client interactions.

The shutdown of North American airspace and a nearly 20% reduction in air travel capacity further exacerbated financial difficulties within the U.S. airline sector.

Moreover, these events precipitated U.S. military interventions in Afghanistan and Iraq, accompanied by an increase in homeland security expenditures totaling no less than $5 trillion.

Effects in Afghanistan

At the time of the attacks, much of the Afghan population was already suffering from severe food shortages. In their wake, tens of thousands attempted to escape in anticipation of U.S. military retaliation. Pakistan—home to many Afghan refugees from previous conflicts—closed its border on September 17, 2001. Thousands also sought refuge in Tajikistan but were refused entry. Taliban officials appealed against military action, highlighting two decades of conflict and ongoing humanitarian challenges.

Following the attacks, all United Nations expatriates and humanitarian workers departed Afghanistan. Relief operations shifted focus to neighboring countries such as Pakistan, China, and Uzbekistan to prepare for a potential humanitarian emergency amid critically depleted food reserves. The World Food Programme suspended wheat imports on September 12 due to security risks.

Approximately one month after these events, a U.S.-led international coalition initiated efforts to dismantle the Taliban regime for harboring al-Qaeda operatives. Initially cautious, Pakistan eventually granted coalition forces access to its bases and surrendered over 600 suspected al-Qaeda members.

In 2011, under President Obama’s administration, troop withdrawals by the U.S. and NATO began and concluded in 2016. Subsequently, during the Trump and Biden administrations, all remaining U.S. and NATO forces exited Afghanistan by August 30, 2021, bringing an end to nearly two decades of conflict. President Biden conceded that after almost twenty years of warfare, establishing Afghanistan as a modern democratic state was unachievable.

Cultural impact

In the immediate aftermath of 9/11, there was a noticeable shift towards prioritizing family life, a rise in church participation, and an upsurge in patriotic expressions, including the widespread display of American flags. The radio industry reacted by removing certain tracks from airplay, while the attacks have since shaped themes in film, music, literature, and television that explore post-9/11 societal anxieties.

Although lacking endorsement from specialists, conspiracy theories surrounding 9/11 have evolved into a widespread social phenomenon. The events also profoundly influenced religious beliefs: some individuals experienced a reinforcement of faith as a means to cope with grief, whereas others questioned or abandoned their spiritual convictions.

American culture following 9/11 is characterized by increased demands for security and pervasive fears about potential future terrorist incidents. Psychological studies have documented heightened national anxiety linked to commercial aviation. Furthermore, hate crimes targeting Muslims surged nearly tenfold in 2001 and have persisted at levels approximately five times higher than those before the attacks.

Anti-terrorism government measures

In response to the attacks, numerous governments introduced new laws aimed at preventing terrorism. In Germany—where several 9/11 hijackers had previously lived—two significant anti-terrorism legislative packages were enacted to close legal gaps that allowed terrorists to reside and fundraise, while enhancing intelligence sharing and law enforcement cooperation. Canada passed its inaugural anti-terrorism statute, the Canadian Anti-Terrorism Act. The United Kingdom enacted the Anti-terrorism, Crime and Security Act 2001 along with the Prevention of Terrorism Act 2005. New Zealand implemented the Terrorism Suppression Act 2002.

Within the United States, the Homeland Security Act of 2002 led to the formation of the Department of Homeland Security to centralize domestic counterterrorism initiatives. The USA Patriot Act broadened federal authority to detain foreign terrorism suspects without charges for up to seven days, monitor communications extensively, and prosecute terror suspects indefinitely. The Federal Aviation Administration mandated reinforced cockpit doors and deployed sky marshals aboard flights. The Aviation and Transportation Security Act transferred airport security oversight to the federal government, establishing the Transportation Security Administration (TSA) responsible for passenger and baggage screening—resulting in longer wait times and privacy debates.

After disclosures in 2013 regarding NSA surveillance programs like PRISM, concerns arose about potential abuses stemming from expanded Patriot Act powers; even its original proponent admitted to excessive measures.

Critiques of the global war on terror have questioned its ethical justification, efficacy, and financial burden. A 2021 report by the Costs of War Project estimated that U.S.-led post-9/11 conflicts displaced nearly 38 million people across Afghanistan, Pakistan, Iraq, Libya, Syria, Yemen, Somalia, and the Philippines. These wars caused roughly 897,000 to 929,000 direct fatalities and incurred costs totaling $8 trillion. A 2023 update projected between 3.6 and 3.7 million indirect deaths in these regions—accounting for infrastructure breakdowns and health emergencies—raising total mortality figures to approximately 4.5 to 4.6 million.

Despite U.S. legislation banning torture, human rights abuses occurred under "enhanced interrogation" programs during counterterror operations. In 2005, reports exposed CIA-run secret detention facilities ("black sites") and covert flights transporting detainees to countries known for torture practices—a method condemned as "torture by proxy."

Legal proceedings

President Obama declared the death of Osama bin Laden, who was killed by U.S. special operations forces on May 2, 2011, at his Abbottabad, Pakistan residence, bringing to a close a decade-long pursuit. Since all 19 hijackers perished in the attacks, they were never brought to trial, and bin Laden was never officially charged.

The primary case against Khalid Sheikh Mohammed and his associates Walid bin Attash, Ramzi bin al-Shibh, Ammar al-Baluchi, and Mustafa Ahmad al Hawsawi remains unresolved. Mohammed was captured in Pakistan in 2003 and detained at secret CIA facilities and Guantanamo Bay, where he underwent interrogation techniques including waterboarding. Mustafa al-Hawsawi and Abd al-Aziz Ali were also apprehended and charged with providing financial and logistical support to the hijackers. During hearings in 2007, Mohammed admitted full responsibility for orchestrating the attacks, stating he "was responsible for the 9/11 operation from A to Z."

In early 2023, efforts by the U.S. government to negotiate plea agreements for the defendants were underway; however, by September 2023, President Biden discontinued these negotiations.

Only a few peripheral individuals connected to the attacks have been convicted:

• Zacarias Moussaoui was indicted in December 2001 and received a life sentence without parole in May 2006.
• Mounir El Motassadeq was found guilty in Germany in 2003 and deported to Morocco after completing his sentence in 2018.
• Abu Dahdah was sentenced by a Spanish court and released in 2013.

Reports from July 2024 indicated that Mohammed, Walid bin Attash, and Mustafa al-Hawsawi had agreed to plead guilty to conspiracy charges in exchange for life imprisonment sentences, thereby avoiding trial and possible execution. Nevertheless, U.S. Defense Secretary Lloyd Austin rescinded this plea deal shortly thereafter.

FBI

Following the attacks, the Federal Bureau of Investigation (FBI) initiated PENTTBOM, the largest criminal investigation ever conducted in the United States. At its height, more than half of all FBI agents were dedicated to this inquiry, pursuing over 500,000 leads. The agency concluded there was "clear and irrefutable" proof linking al-Qaeda and bin Laden to the events.

The FBI rapidly identified several hijackers, including ringleader Mohamed Atta when his luggage was discovered at Boston's Logan Airport. Due to a new policy aimed at preventing flight delays, two checked bags containing documents with hijacker names, assignments, and al-Qaeda affiliations did not board Flight 11. These items became critical evidence often referred to as the "Rosetta stone" of the investigation. Within hours of the attacks, the FBI publicly released names and personal details of suspected hijackers. Abu Jandal, bin Laden’s former chief bodyguard imprisoned since 2000, confirmed during FBI interrogations that seven hijackers were members of al-Qaeda. On September 27, photographs of all 19 hijackers were made public; among them were fifteen Saudis, two from the United Arab Emirates, one Egyptian, and one Lebanese.

By midday on September 11, communications intercepted by the U.S. National Security Agency and German intelligence pointed towards Osama bin Laden’s involvement. Two hijackers had traveled with an associate of bin Laden to Malaysia in 2000; Atta had previously visited Afghanistan and belonged to a Hamburg-based terrorist cell connected to Khalid Sheikh Mohammed.

Electronic surveillance obtained by U.S. and UK agencies also revealed that Mohammed Atef, a deputy to bin Laden, played a significant role in planning the attacks. Conversations intercepted days before September 11 referenced "an incident" occurring in America around that time frame and discussed possible consequences without specifying targets.

In its annual violent crime report for 2001, the FBI classified fatalities from the attacks as murder but separated these figures from other criminal data to prevent distortion of statistics. The bureau noted that including these deaths with standard crime data would compromise analytical accuracy. Likewise, New York City excluded these deaths from its official crime statistics for that year.

CIA

In 2004, John L. Helgerson, serving as the Inspector General of the Central Intelligence Agency (CIA), carried out an internal investigation that sharply criticized high-ranking CIA officials for their inadequate response to terrorism prior to 9/11. Helgerson pointed out the agency's inability to prevent hijackers Nawaf al-Hazmi and Khalid al-Mihdhar from entering the United States and its failure to share critical intelligence with the FBI.

By May 2007, a group of bipartisan senators introduced legislation advocating for the public release of this review, underscoring the importance of transparency regarding the CIA’s activities before the attacks. The report was ultimately made public in 2009 under President Barack Obama’s administration.

Congressional inquiry

In February 2002, the Senate and House Intelligence Committees initiated a joint investigation into the performance of U.S. intelligence agencies both before and after 9/11. Their extensive 832-page report, issued in December 2002, revealed shortcomings by both the FBI and CIA in acting on intelligence about terrorists known to be present in the country. The inquiry also identified potential links involving Saudi officials based on unclassified information; however, 28 pages related to this aspect remained classified at the insistence of the Bush administration.

Bob Graham, chairing the inquiry, disclosed evidence suggesting foreign government support for terrorist operations within the U.S. Families of victims and certain congressional members demanded full transparency by calling for the release of the redacted sections. The Saudi government also advocated for declassification.

In June 2016, then-CIA Director John Brennan expressed optimism that these redacted pages would soon be disclosed publicly and would clear Saudi Arabia of any involvement in the attacks.

Later that year, in September 2016, Congress enacted the Justice Against Sponsors of Terrorism Act, which allowed families of 9/11 victims to pursue legal action against Saudi Arabia over its alleged complicity in the attacks. This legislation passed despite opposition from President Obama and warnings from Saudi Arabia about potential economic repercussions, including withdrawal of investments from the United States.

9/11 Commission

The National Commission on Terrorist Attacks Upon the United States, commonly referred to as the 9/11 Commission and chaired by Thomas Kean, was formed in late 2002 to examine the events surrounding the attacks, including issues related to preparedness and governmental response. Early appointees such as former Secretary of State Henry Kissinger and former Senator George J. Mitchell resigned shortly after due to conflicts of interest. Subsequently, on December 15, 2002, President Bush appointed former New Jersey governor Thomas Kean as chair.

In July 2004, the commission released its comprehensive 9/11 Commission Report, a detailed 585-page document that concluded al-Qaeda was responsible for orchestrating the attacks. The report identified significant failures across imagination, policy formulation, capabilities, and management within U.S. security and intelligence agencies, highlighting their insufficient coordination that contributed to their inability to prevent the tragedy.

The commission’s findings included numerous recommendations aimed at strengthening national security and enhancing counterterrorism measures. However, by 2011, concerns were raised by commission members that many critical recommendations had yet to be implemented, reflecting persistent weaknesses within America’s security framework.

National Institute of Standards and Technology

The U.S. National Institute of Standards and Technology (NIST) conducted a thorough examination into the collapses of the Twin Towers and 7 World Trade Center, focusing on identifying causes and evaluating fire protection systems to enhance future building safety standards. The inquiry regarding 1 World Trade Center and 2 World Trade Center was finalized in October 2005, while the investigation into 7 World Trade Center concluded in August 2008.

NIST determined that the impact of the airplanes stripped away fireproofing materials from the steel framework of the Twin Towers, a factor likely contributing to their failure; had this protective layer remained intact, the buildings might have resisted collapse. Supporting this, a 2007 study by Purdue University demonstrated that the removal of thermal insulation exposed structural girders and columns to intense heat from office fires, weakening them sufficiently to cause collapse irrespective of the initial column damage.

The lead investigator remarked that "the towers performed remarkably well," underscoring that fire, rather than the plane impacts, was responsible for bringing down the buildings. The fires compromised the floor-supporting trusses, causing floors to sag and exert inward forces on exterior columns. This effect, combined with damage sustained by core columns, resulted in buckling of the outer columns and eventual structural failure. Additionally, the report noted that stairwells lacked adequate reinforcement above impact zones, impairing emergency evacuation capabilities.

Regarding 7 World Trade Center, NIST concluded that uncontrolled fires heated floor beams and girders to a point where a key support column failed, triggering a progressive collapse driven by fire.

Alleged Saudi government role

In July 2016, the Obama administration declassified "File 17," a document listing approximately thirty-six individuals, including suspected Saudi intelligence operatives associated with Saudi Arabia’s embassy in Washington, D.C., linking the kingdom to the 9/11 hijackers.

Subsequently, in September 2016, Congress enacted the Justice Against Sponsors of Terrorism Act (JASTA), which authorized families of 9/11 victims to file civil lawsuits against Saudi Arabia for its purported involvement. By March 2018, a U.S. court permitted such litigation to proceed.

In 2022, relatives of victims acquired videos and a notepad seized from Saudi national Omar al-Bayoumi through British legal proceedings. One video depicted al-Bayoumi hosting a gathering in San Diego attended by hijackers Nawaf al-Hazmi and Khalid al-Mihdhar; another showed him welcoming cleric Anwar al-Awlaki, known for radicalizing American individuals. The notepad contained sketches and calculations possibly related to determining descent speeds toward targets. An FBI memorandum revealed that al-Bayoumi had been a paid collaborator with Saudi Arabia’s General Intelligence Presidency from the late 1990s up until 9/11. As of 2022, he is believed to reside in Saudi Arabia, which continues to deny any involvement in the attacks.

Reconstruction

On the day of the attacks, New York City Mayor Rudy Giuliani declared: "We will rebuild. We will emerge stronger... politically stronger, economically stronger. The skyline will be restored."

Within hours following the tragedy, an extensive search and rescue mission was launched. After months of relentless effort, debris clearance at the World Trade Center site was completed by May 2002. The damaged section of the Pentagon was reconstructed and reoccupied within one year. A temporary World Trade Center PATH station became operational by late 2003, while construction of the new 7 World Trade Center wrapped up in 2006. Redevelopment of the main site faced delays until late 2006 when leaseholder Larry Silverstein reached financing agreements with the Port Authority of New York and New Jersey. Construction on One World Trade Center commenced in April 2006 and achieved its full structural height in May 2013 with installation of its spire at 1,776 feet (541 meters), making it the tallest building in the Western Hemisphere. One World Trade Center was completed and opened on November 3, 2014.

Plans included three additional office towers located one block east of the original site. 4 WTC opened in November 2013 as the second tower completed on site and first building on Port Authority land. Following this, 3WTC was finalized in June 2018 as the fourth skyscraper erected at Ground Zero. In December 2022, services resumed fully at the Nicholas Greek Orthodox Church, succeeded by inauguration of the Ronald O. Perelman Performing Arts Center in September 2023. Although construction began on 2 World Trade Center in 2008, it remains incomplete as of 2025. Public presentations of scale models occurred in September 2024 while Silverstein Properties continues efforts to secure funding for this tower’s completion.

Memorials

In the aftermath of the attacks, numerous memorials and vigils were organized worldwide, with photographs of the victims prominently displayed around Ground Zero. President Bush proclaimed September 14, 2001, as Patriot Day in honor of those lost.

One of the earliest tributes was the Tribute in Light, which consists of 88 searchlights projected from the original towers' footprints. In 2006, the World Trade Center Site Memorial Competition selected Reflecting Absence—a design featuring two reflecting pools situated within the towers' foundations, surrounded by an underground space inscribed with victims' names. This memorial was completed to coincide with the tenth anniversary in 2011, and a museum dedicated to the events opened in May 2014.

The Sphere, a large bronze sculpture by Fritz Koenig that once stood between the Twin Towers, survived largely undamaged and was repurposed as a monument commemorating 9/11. After being stored near JFK Airport, it was relocated to Liberty Park, adjacent to the new World Trade Center complex, in August 2017.

The Pentagon Memorial, inaugurated on the seventh anniversary in Arlington County in 2008, features a thoughtfully landscaped park with 184 benches oriented toward the Pentagon. During repairs to the Pentagon from 2001 to 2002, an indoor memorial and private chapel were established at the site where Flight 77 struck.

In Shanksville, Pennsylvania, a visitor center opened in 2015 overlooking the crash location and a white marble Wall of Names. An observation platform aligns precisely beneath Flight 93's flight path. Additionally, New York City firefighters contributed a steel cross constructed from World Trade Center beams, which was installed near the crash site in 2008. Numerous other permanent memorials are found across the United States; families of victims and related organizations have also created scholarships and charitable foundations.

Every year, New York City hosts readings of victims' names; meanwhile, at the Pentagon, the U.S. President participates in a commemorative service and leads a moment of silence on Patriot Day. Smaller ceremonies are held in Shanksville, usually attended by the First Lady. In 2023, President Joe Biden marked the anniversary distinctively by observing it in Anchorage, Alaska—the first time a sitting president commemorated it outside traditional locations since the attacks.