Al-Qaeda executed the September 11 attacks.
The Twin Towers of the World Trade Center collapsed on September 11 , 2001 , as a result of being struck by two jet airliners hijacked by 10 terrorists affiliated with al-Qaeda , during the September 11 attacks . September 11 attacks . Four passenger airliners operated by two major U.S. passenger air carriers ( United Airlines and American Airlines ) -- all of which departed from airports in the northeastern United States bound for California -- were hijacked by 19 al-Qaeda terrorists . Within an hour and 42 minutes , both 110-story towers collapsed , with debris and the resulting fires causing partial or complete collapse of all other buildings in the World Trade Center complex , including the 47-story 7 World Trade Center tower , as well as significant damage to ten other large surrounding structures . United Airlines Flight 93 was a domestic scheduled passenger flight that was hijacked by four Al-Qaeda terrorists on board , as part of the September 11 attacks .