By JOHN SOLOMON and TED BRIDIS, Associated Press Writers

WASHINGTON - Surveillance video from Washington Dulles International 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 crashed into the Pentagon

The video shows an airport screener hand-checking the 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.

The disclosure of the video comes one day before the release of the final report by the Sept. 11 commission, which is expected to include a detailed accounting of the events that day.

Details in the grainy video are difficult to distinguish. But an earlier report by the commission describing activities at Dulles is consistent with the men's procession through airport security as shown on the video.

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.

All 58 passengers �?including the hijackers �?and six crew members, along with 125 employees at the Pentagon, died when the flight crashed into the Pentagon at 9:39 a.m. on Sept. 11, 2001.

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.

Al-Mihdhar and Nawaf al-Hazmi had been known to be associated with al-Qaida since early 1999 by the National Security Agency, and were put on a terrorism watch list on Aug. 24, 2001.

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.

Moments after Hanjour passed alone through the security checkpoint, wearing dark slacks and a short-sleeved shirt, the final two hijackers, the al-Hazmi brothers, walked through the checkpoint.

Nawaf al-Hazmi, described by investigators as the right-hand accomplice of hijacker-planner Mohammed Atta, set off two metal-detectors, and a screener manually checked him with a handheld device.

Nawaf and his brother, each wearing slacks and Oxford shirts, were directed to a nearby counter, where they appeared to examine their tickets while another screener checked Nawaf's carryon bag with an explosive trace detector. Each was cleared to board Flight 77.

The Associated Press 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.

"Even after setting off these alarms, the airlines and security screeners failed to examine the hijackers' baggage, as required by federal regulations and industry mandated standards, or discover the weapons they would use in their attack," lawyer Ron Motley said.

Elaine Teague, one of the family members suing over the death of her 31-year-old daughter, Sandra, said she had previously been shown the footage by the FBI . But the terrorists' faces had been digitally disguised.

Teague said she was surprised at how relaxed security was, given that airlines had received three warnings from the Federal Aviation Administration . One such warning, issued in June 2001, cited "unconfirmed reports that American interests may be the target of a terrorist threat from extremist groups."