THE video footage acquired by the Associated Press newsagency at Dulles Airport shows hijackers Khalid al-Mihdhar and Majed Moqed, each dressed in trousers and collared shirts, setting off metal detectors as they pass through security around 7:18am.

Some of the hijackers who crashed a jetliner into the Pentagon on September 11, 2001, twice set off alarms as they passed through airport metal detectors, but security screeners did not appear to question them about knives they were apparently carrying, according to a newly disclosed surveillance video.

Surveillance video from Washington Dulles International Airport the morning of September 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 crashed into the Pentagon.

Their unsigned Visa debit card was rejected by the travel agency computer, and the clerk would not let them write a cheque for the two first-class airline tickets to Los Angeles they wanted to buy.

US authorities have charged the first person with helping the New York and Washington terrorist hijackers as the number of people arrested or detained in the wide-ranging investigation grew to 352.