Since the attack, the FBI has extended its investigation to dozens of flight schools coast to coast, including some of the same schools it visited in the years before the attack. According to law enforcement officials and press reports, the 19 suspected terrorists received flight training from at least 10 U.S. flight schools. At least 44 people sought by the FBI for questioning received some flight instruction.

[Richard Kaylor] said two FBI agents came to interview him about [Abdul Hakim Murad] in 1996. He said he provided information about Murad and two other student pilots, both of whom lived with Murad. Kaylor said the three men had come to Schenectady after a stint at Alpha Tango Flying Services in San Antonio.

About three years later, FBI agents visited Airman Flight School in Oklahoma to inquire about Ihab Ali Nawawi, a bin Laden associate whose name surfaced during the trial for the 1998 embassy bombings. [Dale Davis], the flight school's director of operations, said Nawawi obtained his commercial pilot's license from Airman in the early 1990s, then traveled to another school in Oklahoma City to qualify for a rating to fly small business aircraft.