http://en.wikipedia.org/wiki/Organizers_of_the_September_11%2C_2001_attacks :
Suspected hijackers
Minutes after the occurrence of the September 11, Terrorist attacks, the Federal Bureau of Investigation opened the largest FBI investigation in United States history, operation PENTTBOM. The suspects were identified within 72 hours because few made any attempt to disguise their names on flight and credit card records and they were among the few non-U.S. citizens and nearly the only passengers with Arabic names on their flights, enabling the FBI to identify their names and in many cases such details as dates of birth, known, and/or possible residences, visa status, and specific identification of the suspected pilots within hours.<9> On September 27, 2001 the FBI released photos of the 19 hijackers, along with information about many of their possible nationalities and aliases <10>.
All the suspected hijackers were from Saudi Arabia, United Arab Emirates, Lebanon or Egypt.United Airlines Flight 175: Marwan al-Shehhi (from the United Arab Emirates), Fayez Banihammad (from the United Arab Emirates), Mohand al-Shehri (Saudi Arabian), Hamza al-Ghamdi (Saudi Arabian), Ahmed al-Ghamdi (Saudi Arabian). They were the only people with Arabic names on the flight.
American Airlines Flight 11: Mohamed Atta al Sayed (Egyptian), Waleed al-Shehri (Saudi Arabian), Wail al-Shehri (Saudi Arabian), Abdulaziz al-Omari (Saudi Arabian), Satam al-Suqami (Saudi Arabian). There was only one other passenger with an Arabic name who was ruled out as having any role.
United Airlines Flight 93: Ziad Jarrah (Lebanese), Ahmed al-Haznawi (Saudi Arabian), Ahmed al-Nami (Saudi Arabian), Saeed al-Ghamdi (Saudi Arabian). They were the only people with Arabic names on the flight.
American Airlines Flight 77: Hani Hanjour (Saudi Arabian), Khalid al-Mihdhar (Saudi Arabian), Majed Moqed (Saudi Arabian), Nawaf al-Hazmi (Saudi Arabian), Salem al-Hazmi (Saudi Arabian). There was one other passenger with an Arabic name who was ruled out as having any role.