From the History Commons Groups blog:

A large number of entries have been added to the Complete 9/11 Timeline at History Commons, many of them providing important details about the events of September 11, 2001, and others describing notable incidents that took place before and after 9/11.

Hijackers Were Recorded on Video at Dulles Airport

The majority of the new entries describe events that took place on September 11. A number of them describe the arrival of the five alleged hijackers of Flight 77 at Washington's Dulles International Airport.

Khalid Almihdhar and Majed Moqed were the first of the hijackers to check in at the American Airlines ticket counter at the airport. Minutes later, the two men entered the airport's west security checkpoint and, despite setting off alarms when they walked through the metal detectors, were cleared to proceed on their way.