On September 11 , 2001 , 19 terrorists associated with the Islamist militant group al-Qaeda hijacked four passenger jets in a series of suicide attacks on the United States , killing 2,996 people and injuring more than 6,000 others . Hijackers flew planes into two main towers of the World Trade Center , resulting in the collapse of three buildings of the World Trade Center complex , and the Pentagon , resulting in the partial destruction of the western side in the building . The resulting dust cloud due to the collapse of the World Trade Center covered Manhattan for days and contained thousands of tons of toxic debris , including asbestos and other known carcinogens . Another hijacked plane crashed into a field in Shanksville , Pennsylvania following an attempt by the passengers to retake control of the plane . No one in the airliners survived
Another hijacked plane
United Airlines Flight 93
World Trade Center Health Program