In Unsafe at any Altitude the authors (Joe and Susan Trento) detail the account of Eric Gill who worked a security checkpoint at Dulles. Gill said that on 9/10 he got into a confrontation with several men trying to enter an employees only door. The problem was that only a couple of the men had valid security cards. Gill told the the men without ID cards they couldn't go through the door. One man got upset and after a brief argument with Gill all the men decided to leave. Later, Gill identified the man who got upset as Nawaf al-Hazmi (alleged Flight 77 hijacker) and identified one of the other men as Marwan al-Shehhi (alleged hijacker/pilot of Flight 175 out of Logan). At the time al-Hazmi was on several government watchlists and al-Shehhi may have been as well.
This story has never gotten much attention but IF TRUE it calls into question key aspects of the 9/11 Commission account. Obviously it makes no sense for radical Islamic al Qaeda operatives posing as Dulles employees to draw attention on the night before the attacks. It also raises the question as to whether weapons were placed on the planes by al Qaeda operatives and/or intelligence officials posing as airline employees. To my knowledge, there were two accounts of possible gun use...Suqami shooting Daniel Lewin (Flight 11) and Tom Burnett (Flight 93) told his wife one of the hijackers had a gun.
One theory is that al-Hazmi was a GID agent which would explain his cavalier use of his real name despite being identified by the CIA back in January 2000. So if Gill's account is true that could mean al-Hazmi the GID agent had no intention of boarding a plane on 9/11. He could have been betrayed by his handlers, killed and then added to the Flight 77 flight manifest later. Yes, I realize this is speculative and am not making any assertion of fact.