Hazmi had a relatively long history with al-Qaeda before being selected for the attacks. He obtained a tourist visa through the Visa Express program and arrived in the United States in June 2001 where he would settle in New Jersey with other American 77 hijackers up until the attacks.
On September 11, 2001, Hazmi boarded American Airlines Flight 77 and helped subdue the passengers and crew for Hani Hanjour, the pilot among the hijackers, to crash the plane into west facade of the Pentagon. His older brother, Nawaf al-Hazmi, was another hijacker aboard the same flight. At the age of 20 years and 221 days he was the youngest hijacker who participated in the attacks.
On September 11, 2001, Hazmi boarded American Airlines Flight 77. Airport surveillance video from Washington's Dulles Airport shows two of the five hijackers, including Salem al-Hazmi, being pulled aside to undergo additional scrutiny after setting off metal detectors.
The flight was scheduled to depart at 08:10, but ended up departing 10 minutes late from Gate D26 at Dulles. The last normal radio communications from the aircraft to air traffic control occurred at 08:50:51. At 08:54, Flight 77 began to deviate from its normal, assigned flight path and turned south, and then hijackers set the flight's autopilot heading for Washington, D.C. Passenger Barbara Olson called her husband, United States Solicitor General Theodore Olson, and reported that the plane had been hijacked and that the assailants had box cutters and knives. At 09:37, American Airlines Flight 77 crashed into the west facade of the Pentagon, killing all 64 aboard (including the hijackers), along with 125 on the ground in the Pentagon. In the recovery process at the Pentagon, remains of all five Flight 77 hijackers were identified through a process of elimination, as not matching any DNA samples for the victims, and put into custody of the FBI. Forensics teams confirmed that it seemed two of the hijackers were brothers, based on their DNA similarities.