World Trade Center site
On the morning of September 11, 2001, Islamic terrorists affiliated with Al-Qaeda hijacked American Airlines Flight 11 and United Airlines Flight 175, both which were en route to Los Angeles, and intentionally crashed them into the two main towers of the World Trade Center. The towers collapsed within two hours of the collisions. 2,606 people, including 2,192 civilians, 71 law enforcement officers, and 343 firefighters, who were in the towers and in the surrounding area died in the attacks, as well as 147 civilians and the 10 hijackers aboard the two airliners. After the collapse of the World Trade Center, hospital workers and law enforcement officers began referring to the World Trade Center site as "Ground Zero".
American Airlines Flight 77
On the morning of September 11, 2001, the five hijackers arrived at Washington Dulles International Airport. At 07:15, Khalid al-Mihdhar and Majed Moqed checked in at the American Airlines ticket counter for Flight 77, arriving at the passenger security checkpoint a few minutes later at 07:18. Both men set off the metal detector and were put through secondary screening. Moqed continued to set off the alarm, so he was searched with a hand wand. The Hazmi brothers checked in together at the ticket counter at 07:29.[Hani Hanjour checked in separately and arrived at the passenger security checkpoint at 07:35. Hanjour was followed minutes later at the checkpoint by Salem and Nawaf al-Hazmi, who also set off the metal detector's alarm. The screener at the checkpoint never resolved what set off the alarm. As seen in security footage later released, Nawaf Hazmi appeared to have an unidentified item in his back pocket. Utility knives up to four inches were permitted at the time by the Federal Aviation Administration (FAA) as carry-on items. The passenger security checkpoint at Dulles International Airport was operated by Argenbright Security, under contract with United Airlines.