"Surveillance video from Washington’s Dulles Airport the morning of Sept. 11, 2001, shows four of the five hijackers being pulled aside to undergo additional scrutiny after setting off metal detectors but then permitted to board the fateful flight that later crashed into the Pentagon.
The surveillance video, obtained by The Associated Press, shows an airport screener hand-checking the carryon baggage of one hijacker, Nawaf al-Hazmi, for traces of explosives before letting him continue onto American Airlines Flight 77 with his brother, Salem, a fellow hijacker.
Details in the grainy video are difficult to distinguish. But an earlier report by the commission is consistent with the men’s procession through airport security as shown on the video obtained by the AP.
No knives or other sharp objects are visible on the surveillance video. But investigators on the commission have said the hijackers at Dulles were believed to be carrying utility knives either personally or in their luggage, which at the time could legally be carried aboard planes.
The video shows hijackers Khalid al-Mihdhar and Majed Moqed, each dressed conservatively in slacks and collared shirts, setting off metal-detectors as they pass through security. Moqed set off a second alarm, and a screener manually checked him with a handheld metal detector.
The pair were known to travel together previously and had paid cash to purchase their tickets aboard Flight 77 on Sept. 5, 2001, at the American Airlines counter at Baltimore’s airport.
Only Hani Hanjour, believed to have been the hijacker who piloted Flight 77, did not set off a metal detector as he passed through Dulles security that morning, according to the video.
The AP obtained the video from the Motley Rice law firm, which is representing some survivors’ families who are suing the airlines and security industry over their actions in the Sept. 11 attacks." -ABC (07/21/04)

Is this really the 5 ft. "skinny" Hani Hanjour said to be in this Dulles Airport security clip? 

Dulles Airport security clip of alleged       ATM surveillance clip          FBI photo of Hanjour (unknown date)
Hanjour supposedly taken on 09/11/01    of Hanjour taken on
Yahoo news                                                     09/05/01 (Washington Post)