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, Mohamed Atta, Marwan al-Shehhi, and Ziad Jarrah in mid-2000 to undertake flight training in south Florida. The fourth hijacker-pilot, Hani Hanjour, arrived in San Diego in December 2000. The rest of the "muscle hijackers" arrived in early- and mid-2001.
As for the pilots who would go on to participate in the attacks, three of them were original members of the Hamburg cell (Mohamed Atta, Marwan al-Shehhi and Ziad Jarrah). Following their training at Al-Qaeda training camps in Afghanistan, they were chosen by Bin Laden and Al-Qaeda's military wing due to their extensive knowledge of western culture and language skills, increasing the mission's operational security and its chances for success. The fourth intended pilot, Ramzi bin al-Shibh, a member of the Hamburg cell, was also chosen to participate in the attacks yet was unable to obtain a visa for entry into the United States. He was later replaced by Hani Hanjour, a Saudi national.
Mihdhar and Hazmi were also potential pilot hijackers, but did not do well in their initial pilot lessons in San Diego. Both were kept on as "muscle" hijackers, who would help overpower the passengers and crew and allow the pilot hijackers to take control of the flights. In addition to Mihdhar and Hazmi, thirteen other muscle hijackers were selected in late 2000 or early 2001. All were from Saudi Arabia, with the exception of Fayez Banihammad, who was from the United Arab Emirates.
Bold letters note the hijackers who piloted the planes.
Two flight attendants called the American Airlines reservation desk during the hijacking. Betty Ong reported that "the five hijackers had come from first-class seats: 2A, 2B, 9A, 9C and 9B." Flight attendant Amy Sweeney called a flight services manager at Logan Airport in Boston and described them as Middle Eastern. She gave the staff the seat numbers and they pulled up the ticket and credit card information of the hijackers, identifying Mohamed Atta.