Hamburg cell in the context of "Clandestine cell system"

The aircraft hijackers in the September 11 attacks were 19 men affiliated with al-Qaeda, a jihadist organization based in Afghanistan. They hailed from four countries; 15 of them were citizens of Saudi Arabia, two were from the United Arab Emirates, one was from Egypt, and one from Lebanon. To carry out the attacks, the hijackers were organized into four teams each led by a pilot-trained hijacker who would commandeer the flight with three or four "muscle hijackers" who were trained to help subdue the pilots, passengers, and crew. Each team was assigned to a different flight and given a unique target to crash their respective planes into. Mohamed Atta was the assigned ringleader over all four groups.

The first hijackers to arrive in the United States were Khalid al-Mihdhar and Nawaf al-Hazmi, who settled in San Diego County, California, in January 2000. They were followed by three hijacker-pilots, Hamburg cell members Mohamed Atta, Marwan al-Shehhi, and Ziad Jarrah in mid-2000 to undertake flight training at Huffman Aviation flight-training school in Venice, Florida. The fourth hijacker-pilot, Hani Hanjour, who was not a member of the Hamburg cell, arrived in San Diego in December 2000. The rest of the "muscle hijackers" arrived in early- and mid-2001.

Mohamed Atta (1 September 1968 – 11 September 2001) was an Egyptian engineer and terrorist hijacker for al-Qaeda. Ideologically a pan-Islamist, he was the ringleader of the September 11 attacks and served as the hijacker-pilot of American Airlines Flight 11, which he flew into the North Tower of the original World Trade Center as part of coordinated suicide attacks. Aged 33, he was the oldest of the 19 hijackers who took part in the mission. Before the attacks, he worked as a civil engineer.

Born and raised in Egypt, Atta studied architecture at Cairo University, graduating in 1990, and pursued postgraduate studies in Germany at the Hamburg University of Technology. In Hamburg, Atta became involved with the al-Quds Mosque where he met Marwan al-Shehhi, Ramzi bin al-Shibh, and Ziad Jarrah, together forming the Hamburg cell. Atta disappeared from Germany for periods of time, embarking on the hajj in 1995 but also meeting Osama bin Laden and other top al-Qaeda leaders in Afghanistan from late 1999 to early 2000. Atta and the other Hamburg cell members were recruited by bin Laden and Khalid Sheikh Mohammed for a "planes operation" in the United States.

Marwan al-Shehhi (9 May 1978 – 11 September 2001) was an Emirati terrorist hijacker for al-Qaeda. He was the hijacker-pilot on United Airlines Flight 175 (Boeing 767). As part of the September 11 attacks, he crashed the plane into the South Tower of the World Trade Center in a suicide attack. He was one of five hijackers aboard the aircraft and one of two Emiratis to take part in the attacks, the other being Fayez Banihammad, who helped him hijack the same plane.

Al-Shehhi was a university student in applied sciences from the United Arab Emirates. In 1996, at the age of 18, he moved to Germany to pursue his university education. There, he met Mohamed Atta and Ziad Jarrah, who were also studying applied sciences and engineering. Shortly thereafter, Ramzi bin al-Shibh, who provided them with financial support, joined them, and they formed the Hamburg cell. Together, after pledging their lives to martyrdom (Jihad), they became the leaders of the September 11 attacks.

Ziad Samir Jarrah (Arabic: زياد سمير جراح; 11 May 1975 – 11 September 2001), also known as Ziad al-Jarrah, was a Lebanese terrorist who was a member of al-Qaeda, a pan-Islamist militant organization. During the 11 September attacks in 2001, he was one of 19 al-Qaeda members who hijacked four American commercial flights in an attempt to crash them into national landmarks in the country. Jarrah's group hijacked United Airlines Flight 93, departing Newark, New Jersey, for San Francisco, but they failed to reach their target when the plane crashed.

Jarrah grew up in a secular and wealthy family living in Beirut during the Lebanese Civil War (1975-1990). In 1996, he moved to Germany to study aerospace engineering at the Hamburg University of Applied Sciences. In Hamburg, he became part of a clandestine cell system known as the Hamburg cell with fellow hijackers Mohamed Atta and Marwan al-Shehhi, among many others. In 1999, member Ramzi bin al-Shibh took the cell to Afghanistan to meet al-Qaeda's leader, Osama bin Laden, where they were instructed to receive flight training. In 2000, Jarrah enrolled in a flight school in Florida.

The al-Quds Mosque (Arabic: مسجد القدس, romanized: Masjid al-Quds, lit. 'The Jerusalem Mosque'; German: al-Quds-Moschee) was a Sunni Islam mosque, located in Hamburg, Germany. The mosque was opened in 1993 and operated until 2010 when it was shut down by German security officials.

The mosque was known for preaching a radical form of Sunni Islam. The al-Quds Mosque was attended by some of the September 11 attackers including Mohamed Atta, Marwan al-Shehhi, Ramzi bin al-Shibh, and Ziad Jarrah who formed the Hamburg cell.

Ramzi Mohammed Abdullah bin al-Shibh (Arabic: رمزي محمد عبد الله بن الشيبة, romanized: Ramzī Muḥammad ʻAbd Allāh bin al-Shībh; born May 1, 1972) is a Yemeni terrorist who served as al-Qaeda's communications officer. He has been detained by the United States in the Guantanamo Bay detention camp (NSGB) since 2006. He is accused of being a "key facilitator" for the September 11 attacks in 2001.

In the mid-1990s, bin al-Shibh moved as a student to Hamburg, Germany, where he allegedly became close friends with Mohamed Atta, Ziad Jarrah, and Marwan al-Shehhi. Together, they are suspected of forming the Hamburg cell and becoming central perpetrators of the September 11 attacks. He was the only one of the four who failed to obtain a U.S. visa; he is accused of acting as an intermediary for the hijackers in the United States, by wiring money and passing on information from key al-Qaeda figures. After the attacks, bin al-Shibh was the first to be publicly identified by the U.S. as the "20th hijacker", for whom there have been several more possible candidates.