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Islamist extremist group, that occurred on the morning of September 11, 2001.
The attacks killed 2,977 people. (Read More)
Shown in this combo image are two documentations of the September 11, 2001, terrorist attack in New York City and the current day location. (Top) The south tower starts to collapse as smoke billows from both buildings of the World Trade Center in New York. (Below) The skyscraper known as One World Trade Center rises in the lower Manhattan skyline, Aug. 4, 2011 in New York. (AP Photo/ Jim Collins (Top), Mark Lennihan (Bottom))
Remembering 9/11
President Barack Obama, flanked by Defense Secretary Leon Panetta, left, and Joint Chiefs Chairman Gen. Martin Dempsey, bow their heads at the Pentagon Memorial,Tuesday, Sept. 11, 2012, during a ceremony to mark the 11th anniversary of the Sept. 11 attacks. (AP Photo/Carolyn Kaster)
Teneal Colbert, 15, right, her brother Fredrick Meeks, 9, left and brother Tyrus Colbert, 14, top left, of Garden City, N.Y., watch a large monitor broadcasting ceremonies near the World Trade Center site Sunday, Sept. 11, 2011 as the 10th anniversary of the attacks on the World Trade Center is marked in New York. (AP Photo/Craig Ruttle)
