On July 10, 2001, “An FBI agent in the Phoenix field office [Kenneth Williams] sent a memo to FBI headquarters and to two agents on international terrorism squads in the New York Field Office, advising of the ‘possibility of a coordinated effort by Usama Bin Ladin’ to send students to the United States to attend civil aviation schools. The agent based his theory on the ‘inordinate number of individuals of investigative interest’ attending such schools in Arizona. The agent made four recommendations to FBI headquarters: to compile a list of civil aviation schools, establish liaison with those schools, discuss his theories about Bin Ladin with the intelligence community, and seek authority to obtain visa information on persons applying to flight schools. His recommendations were not acted on. His memo was forwarded to one field office. Managers of the Usama Bin Ladin unit and the Radical Fundamentalist unit at FBI headquarters were addressees, but they did not even see the memo until after September 11. No managers at headquarters saw the memo before September 11, and the New York Field Office took no action.”
– 9/11 Commission, The 9/11 Commission Report, Page 272