23 years of mourning: 9/11 terrorist attacks on America (69 images)

By UPI Staff

It's been 23 years since September 11, 2001, when terrorists orchestrated by Osama bin Laden hijacked four passenger planes. They flew two in the World Trade Center in New York City and one into the the Pentagon outside Washington, D.C., while the other crashed into a field in rural Pennsylvania after the crew and passengers fought the attackers. A total of 2,977 people were killed. Here's a look back at that day and two decades of remembrances.

Rays of light burst off a building at 1 Liberty Plaza to silhouette two firefighters surveying Ground Zero at dawn on September 15, 2001. Photo by Chris Corder/UPI

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People watch the World Trade Center burn as they listen to the radio of a stopped taxi following a terrorist attack involving two airplanes flying into the twin towers in New York City on September 11, 2001. Photo by Monika Graff/UPI

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President George W. Bush watches television coverage of the attacks on the World Trade Center on September 11, 2001, as he is briefed in a classroom at Emma E. Booker Elementary School in Sarasota, Fla. Bush was visiting the children when he got news of the attacks. Photo by Eric Draper/George W. Bush Presidential Library

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The twin towers of the World Trade Center billow smoke after two airplanes crashed into the buildings on September 11, 2001. Photo by Laura Cavanaugh/UPI

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