<Tr> <Th> Perpetrators </Th> <Td> Al - Qaeda (see also responsibility and hijackers) </Td> </Tr> <Tr> <Th> No. of participants </Th> <Td> 19 </Td> </Tr> <P> The September 11 attacks (also referred to as 9 / 11) were a series of four coordinated terrorist attacks by the Islamic terrorist group al - Qaeda on the United States on the morning of Tuesday, September 11, 2001 . The attacks killed 2,996 people, injured over 6,000 others, and caused at least $10 billion in infrastructure and property damage . </P> <P> 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 . Two of the planes, American Airlines Flight 11 and United Airlines Flight 175, were crashed into the North and South towers, respectively, of the World Trade Center complex in New York City . 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 . A third plane, American Airlines Flight 77, was crashed into the Pentagon (the headquarters of the United States Department of Defense) in Arlington County, Virginia, leading to a partial collapse of the building's western side . The fourth plane, United Airlines Flight 93, was initially steered toward Washington, D.C., but crashed into a field in Stonycreek Township near Shanksville, Pennsylvania, after its passengers tried to overcome the hijackers. 9 / 11 was the single deadliest incident for firefighters and law enforcement officers in the history of the United States, with 343 and 72 killed respectively . </P>

What day of the week did september 11th happen