Planning of the September 11 attacks
On September 11, 2001, a group of 19 al-Qaeda operatives commandeered four commercial jets, transforming them into instruments for synchronized suicide attacks aimed at the World Trade Center in New York City, the Pentagon near Arlington, Virginia, and a fourth target believed to be the United States Capitol. Two of these aircraft crashed into the World Trade Center towers, one struck the Pentagon, while the last plane went down in Pennsylvania after passengers attempted to regain control. These assaults caused 2,977 fatalities, constituting the most lethal foreign assault on American soil, exceeding the casualties of the 1941 Pearl Harbor attack. The operation was carefully orchestrated by al-Qaeda, which assigned terrorists to hijack Boeing 757 and 767 planes operated by American Airlines and United Airlines.
Background
Al-Qaeda was established in 1979 following the Soviet invasion of Afghanistan. Osama bin Laden traveled to Afghanistan to collaborate with Palestinian-Jordanian Abdullah Azzam in organizing Arab mujahideen fighters. In 1984, they co-founded Maktab al-Khidamat (MAK) to facilitate support for Arab volunteers joining the Afghan jihad.
By the late 1980s, as Soviet troops withdrew, bin Laden and Azzam debated MAK’s direction. Both sought to defend oppressed Muslims worldwide. Bin Laden pushed for training in terrorist methods, whereas Azzam opposed violence against women or children on religious grounds and issued a fatwa forbidding such acts.
In November 1989, following their split, Azzam was killed by a remote-detonated bomb in Peshawar, Pakistan. Although bin Laden’s role remains unproven, Azzam’s death allowed bin Laden to take full command of MAK, effectively founding al-Qaeda. Under Dr. Ayman al-Zawahiri’s influence, bin Laden adopted increasingly extremist views.
After Saudi Arabia declined bin Laden’s offer to defend against Saddam Hussein during the Gulf War in 1990 and criticized the Saudi monarchy for permitting U.S. troops on its soil, bin Laden was expelled to Sudan by 1991. There he directed operations across East Africa, including the 1993 attack on U.S. forces in Mogadishu, Somalia. Due to international pressure, Sudan forced him out in 1996, leading to his relocation back to Afghanistan.
Ideology
The Iraqi invasion of Kuwait in 1990 marked a pivotal change in bin Laden’s focus toward opposing the United States. He condemned the Saudi regime for hosting approximately 500,000 U.S. troops and instead promoted a mujahideen campaign to drive out Iraqi forces. Bin Laden viewed the sustained U.S. military presence in Saudi Arabia as religiously forbidden—interpreting Islamic law as prohibiting a "permanent presence of infidels" within Arabian lands. This belief fueled attacks on American military assets in Saudi Arabia, including the embassy bombings in Kenya in 1998, which coincided with the eighth anniversary of U.S. deployment there.
Bin Laden labeled the Saudi royal family as apostates and criticized U.S. alliances with Kuwait, Jordan, and Egypt. He considered Israelis illegitimate occupiers within Muslim territories and condemned U.S. foreign policies that supported Israel, identifying prominent members of the Clinton administration as key proponents of this pro-Israel orientation.
Fatwas
In 1996, bin Laden issued a fatwa demanding the withdrawal of U.S. forces from Saudi Arabia. While fatwas are customarily declared by Islamic religious authorities, bin Laden employed them as political tools to mobilize followers. The 1998 bombings of U.S. Embassies marked a significant intensification of his campaign against the United States, which was followed by a February 1998 fatwa co-authored with Ayman al-Zawahiri that openly declared war on America, designating all Americans—whether military personnel or civilians—as legitimate targets.
Bin Laden justified his stance by citing grievances such as the presence of American troops on Saudi Arabia’s sacred soil, the devastating sanctions imposed on Iraq after the Gulf War, and U.S. backing of Israel. In a 1999 interview, he reaffirmed his opposition to American military deployment near Mecca, perceiving it as an affront to Muslims globally, and criticized Israel’s actions against Palestinians, which he claimed were financed by U.S. funds.
Origins of the September 11 attacks
The conception of the September 11 attacks drew inspiration from the Bojinka plot, a terrorist scheme developed by Khalid Sheikh Mohammed and his nephew Ramzi Yousef, who was also responsible for the 1993 World Trade Center bombing. This plan entailed bombing eleven trans-Pacific flights and crashing an aircraft into the CIA Headquarters. In 1994, Yousef tested part of this plot by planting a bomb on Philippine Airlines Flight 434, which exploded but resulted in only one fatality. The conspiracy was exposed after a fire destroyed Yousef’s apartment in Manila, leading authorities to seize his laptop containing detailed plans. Yousef was subsequently apprehended by U.S. and Pakistani forces in 1995.
In 1996, Khalid Sheikh Mohammed presented an adapted version of this plan to bin Laden while in Afghanistan. According to the 9/11 Commission, Mohammed proposed hijacking ten planes departing from both coasts of the United States; nine would be flown into prominent targets such as the World Trade Center, The Pentagon, United States Capitol, CIA Headquarters, FBI Headquarters, tallest skyscrapers in California and Washington State, along with an unspecified nuclear facility. The tenth plane would be piloted by Mohammed himself; he planned to eliminate adult male passengers onboard, land at a U.S. airport, deliver a speech condemning American policies, and then release the remaining passengers. Bin Laden initially dismissed this proposal as overly complicated.
In December 1998, the Director of Central Intelligence Counterterrorist Center alerted President Bill Clinton that al-Qaeda was actively preparing attacks within the United States, including training operatives in aircraft hijacking techniques.
By late 1998 or early 1999, bin Laden gave Khalid Sheikh Mohammed approval to advance a more limited "planes operation." During meetings held in spring 1999 involving Mohammed, bin Laden, and deputy Mohammed Atef, discussions centered on target priorities: Mohammed favored striking the World Trade Center, whereas bin Laden emphasized attacking the White House, Capitol Building, and Pentagon with the intent to disrupt the U.S. government’s stability. Hijackers unable to reach designated targets were instructed to deliberately crash their planes. Bin Laden recommended operatives such as Nawaf al-Hazmi, Khalid al-Mihdhar, Walid Muhammad Salih Bin 'Attash (Khallad), and Abu Bara al-Taizi. The Saudi nationals al-Hazmi and al-Mihdhar had easier access to U.S. visas; meanwhile, Yemenis Khallad and al-Taizi were assigned operations in Asia due to difficulties obtaining visas for America. Upon arrival of Mohamed Atta and other members of the Hamburg cell in Afghanistan, bin Laden selected them for participation in the plot and appointed Atta as its leader.
At this stage, Khalid Sheikh Mohammed headed al-Qaeda’s military committee, offering operational guidance including target selection and facilitating hijacker travel arrangements. He noted that nuclear facilities had been considered prime targets but were ultimately excluded out of concern that the plan might escalate beyond control.
Hamburg cell
In 1999, Mohammed Atta, Ramzi bin al-Shibh, Marwan al-Shehhi, and Ziad Jarrah appeared in Kandahar after traveling from Germany. The Hamburg cell was established in 1998 following Atta's endorsement from Al-Qaeda's leadership for the operation. The group comprised Mohamed Atta, Marwan al-Shehhi, Ziad Jarrah, Ramzi bin al-Shibh, Said Bahaji, Zakariyah Essabar, among others.
Atta moved to Germany in 1992 to pursue urban planning studies at the Technical University of Hamburg. During his time there, he became influenced by the strict Sunni Islam practiced at Hamburg's al-Quds Mosque. His religious devotion deepened following a 1995 pilgrimage to Mecca. However, by late 1997, it is believed Atta journeyed to Afghanistan instead of Mecca, where he attended Al-Qaeda training camps in 1999 and 2000.
Ramzi bin al-Shibh, a Yemeni national, initially sought asylum in Germany in 1995 but was denied and returned to Yemen. He later reentered Germany in 1997 under his true identity after obtaining a visa, where he met Atta and shared accommodation with him for two years. In late 1999, bin al-Shibh underwent training at Al-Qaeda camps in Kandahar. Although originally intended as a hijacker pilot alongside Atta, al-Shehhi, and Jarrah, he was refused U.S. visas on four occasions due to concerns about visa overstays by Yemenis. After failing to gain entry to the U.S., he assumed a coordination role linking Atta with Khalid Sheikh Mohammed.
Marwan al-Shehhi arrived in Bonn in 1996 on a scholarship from the UAE Army to study marine engineering. He encountered Atta in 1997 and joined the Hamburg cell by 1998. Raised by a father with religious training, al-Shehhi strictly followed Islamic teachings but displayed a more approachable personality compared to the reserved and intense Atta.
Ziad Jarrah came to Germany from Lebanon in 1996, initially attending junior college before transferring to the Technical University of Hamburg in 1997 to study aircraft engineering. His religious beliefs became increasingly radical during this time. In the summer of 1997, he worked at a Volkswagen paint facility.
Other participants included Said Bahaji, who was born in Germany but spent part of his upbringing in Morocco. He enrolled in electrical engineering at the technical university in 1996. His growing extremism led his aunt Barbara Arens to cease weekend visits, recognizing his shift toward radical ideology.
Selection for September 11 plot
In 1999, the group intended to join combat in Chechnya but were advised by Abu Musab in Duisburg, Germany, to instead travel to Afghanistan for training. Later that year, they pledged allegiance to bin Laden and committed to a covert mission involving flight instruction. Bin Laden appointed Atta as leader and personally selected all hijackers together with Mohammed Atef. At this point, the team also included Nawaf al-Hazmi and Khalid al-Mihdhar, who had been chosen earlier by bin Laden.
Atta, al-Shehhi, and Jarrah acquired new passports prior to submitting applications for U.S. visas. By early 2000, Atta, Jarrah, and bin al-Shibh returned to Hamburg while al-Shehhi traveled to the UAE for official documents and visa processing. Upon their return to Germany, they distanced themselves from extremist groups and modified their appearances to reduce suspicion.
Arrival in the United States
On January 15, 2000, al-Mihdhar and al-Hazmi landed in Los Angeles. Shortly thereafter, Marwan al-Shehhi submitted an application for a U.S. visa from the UAE, marking him as the first member of the Hamburg cell to do so.
By June, Atta, Jarrah, and al-Shehhi had also entered the United States. Bin al-Shibh and Essabar repeatedly encountered visa denials; bin al-Shibh shifted his approach from applying for visitor visas to seeking a student visa, including making a $2,200 deposit at a Florida flight school attended by Ziad Jarrah. Despite providing financial documentation and multiple attempts, his visa requests were rejected, prompting him to contribute financially to the cell instead. Meanwhile, Mohammed frequently traveled throughout Southeast Asia. Jarrah nearly withdrew from the operation but was expected to be replaced by Zacarias Moussaoui if he had done so.
Omar al-Bayoumi, who had lived in San Diego since 1995 and was connected to a Saudi aviation company, often recorded videos of various locations and assisted immigrants with housing. In 2000, he hosted Nawaf al-Hazmi and Khalid al-Mihdhar after meeting them in Los Angeles. Al-Bayoumi helped them relocate to San Diego and organized a welcoming gathering; al-Hazmi signed a six-month lease and accessed the internet at the San Diego State University Library.
Although their lease payments were initially covered, it was considered costly. In spring, al-Hazmi arranged for a $5,000 wire transfer from Saudi Arabia through a friend's bank account; these funds were intended for flight instruction. They completed one lesson at Montgomery Field but did not pursue further training. Flight instructor Fereidoun "Fred" Sorbi recalled that they wanted to pilot Boeings immediately but were advised to begin with smaller aircraft.
Al-Hazmi held season passes to local attractions such as the San Diego Zoo and SeaWorld San Diego. The group regularly visited Cheetah's strip club near the Islamic Center and often drove their Toyota sedan on trips to Las Vegas.
Flight training
In March 2000, Mohamed Atta reached out via e-mail to the Academy of Lakeland in Florida, expressing that they were a group from Arab nations residing in Germany seeking intensive pilot training up to the ATP certification level. He sent between 50 and 60 similar inquiries to various U.S. flight schools.
Atta was granted a U.S. visa on May 18, 2000, then traveled through Prague before arriving in Venice, Florida with Marwan al-Shehhi and Ziad Jarrah. They visited Huffman Aviation, voicing dissatisfaction with their previous flight school experience and exploring other options. By December of that year, Atta and al-Shehhi had departed Huffman Aviation; Atta earned his pilot license on December 21. Jarrah left Huffman Aviation on January 15, 2001.
Final preparations
Approximately three weeks prior to the attacks, code names were assigned to their targets: Mohamed Atta designated the U.S. Capitol as "The Faculty of Law," the Pentagon as "The Faculty of Fine Arts," and the World Trade Center as "The Faculty of Town Planning."
Financial backing
The 9/11 Commission estimated that the attackers expended between $400,000 and $500,000 on the operation but were unable to trace the source of these funds, emphasizing the absence of proof for financial support from any foreign government. Prior to 9/11, the CIA approximated Al Qaeda’s yearly operational expenses at about $30 million.
In October 2001, CNN reported that investigators suspected Ahmed Omar Saeed Sheikh (also known as Mustafa Muhammad Ahmad) transferred in excess of $100,000 from Pakistan to Mohamed Atta, who subsequently allocated money to co-conspirators located in Florida. Pakistani authorities reportedly connected Sheikh’s influence to networks extending beyond the ISI, including links with U.S. intelligence agencies.
After this financial transfer came to light, Pakistan’s Inter-Services Intelligence chief, General Mahmood Ahmed, stepped down amid reports of FBI probes into his possible role in authorizing the funds sent to Atta.
On September 11, senior U.S. officials engaged in discussions with General Mahmood Ahmed seeking Pakistan’s collaboration in the "war on terror." Following these talks, Ahmed led a delegation to Kandahar for urgent negotiations with the Taliban aimed at compelling Osama bin Laden’s surrender.
In June 2001, a U.S. intelligence source disclosed that investigations into bin Laden and members of the Saudi royal family faced limitations following the 2000 elections.
By May 2002, former FBI agent Robert Wright Jr. publicly admitted that obstruction by his superiors had impeded his efforts to investigate Al-Qaeda’s financial networks. He later identified shortcomings within the FBI’s International Terrorism Unit concerning Yasin al-Qadi, a Saudi businessman who was subsequently designated as a global terrorist financier.
Yasin al-Qadi was head of the Muwafaq Foundation, an organization connected to bin Laden’s network, and owned Ptech—a software firm providing advanced systems to several U.S. government agencies including the FBI and Pentagon. Matthew Levitt, a former FBI counterterrorism official, voiced concerns about al-Qadi’s access to sensitive information through Ptech. The company’s board included Yacub Mirza and Hussein Ibrahim, both individuals linked by U.S. authorities to radical Islamist groups and accused of channeling funds for Hamas militants.
Senator Bob Graham revealed that two hijackers had support networks within the United States involving Saudi operatives; however, congressional inquiries were obstructed by both the Bush administration and the FBI. Crucial financial information tied to Saudi connections remains classified despite bipartisan appeals for its disclosure.