Khalid al-Mihdhar (1975-2001) was one of the 9-11 Attack hijackers, aboard American Airlines Flight 77 when it crashed into the Pentagon Building. He may have been the closest to identification, before the event, by the United States intelligence community, having been on a watchlist as a known affiliate of al-Qaeda, and having been known to have re-entered the United States.
Maggie Gillespie, an Federal Bureau of Investigation analyst at the Counterterrorism Center, had earlier asked that he and Nawaf al-Hazmi be placed on a watchlist. She passed this to Dina Corsi, another intelligence analyst at FBI headquarters, since Mindhar had reentered the United States. Corsi alerted Jack Cloonan's FBI counterterrorism squad, and Cloonan asked that he be able to use FBI criminal agents since there was an existing indictment against bin Laden; the criminal side of the New York office had far more resources. Corsi emailed back, "If al-Mindhar is located the interview must be intended by an intel agent. A criminal agent CANNOT be present at the interview...If at such time intformation is developed indicating the existence of a substantial federal crime, that information will be passed over the wall according to the proper procedures and turned over for follow-up investigation." 
On Aug. 28, 2001, the FBI began looking for him, based on his connection to the Kuala Lumpur meeting and USS Cole bombing facilitator Khallad. Few resources were assigned to the effort, and he was not located.
- Lawrence Wright (2006), The Looming Tower: Al-Qaeda and the Road to 9/11, Alfred A. Knopf, ISBN 037541486X, pp. 352-354
- The 9-11 Commission Final Report, July 22, 2004, Chapter 8.2.