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This newly released image by the Federal Bureau of Investigation shows a bulldozer removing debris from a U.S. flag in the Pentagon after the crash of American Airlines Flight 77 on September 11, 2001. Five terrorists hijacked American Airlines Flight 77 on September 11, 2001, and flew the 90-ton plane into the Pentagon, killing all passengers and crew on board as well as 125 civilians and military personnel on the ground. Photo: AFP/FBI

First responders at the Pentagon after the crash. In the photos, the immediate devastation after the attack and the fire engulfing the building can be seen. Photo: AFP/FBI

The interior of the Pentagon after the crash. Photo: AFP/FBI

Debris from the American Airlines Flight 77 after it crashed into the Pentagon on September 11, 2001. Photo: AFP/FBI

This undated photo provided by the FBI shows damage to the Pentagon after the attacks. Photo: FBI via AP

This aerial photo shows the site of the attack. Photo: FBI via AP

The flames had melted the office equipment and walls of the building. Photo: FBI via AP

A rescue helicopter surveys damage to the Pentagon as firefighters battle flames after the crash in this September 11, 2001 file photo. Photo: Reuters