FBI agents, fire fighters, rescue workers and engineers work at the Pentagon crash site on Sept. 14, 2001.

FBI agents, fire fighters, rescue workers and engineers work at the Pentagon crash site on Sept. 14, 2001, where a hijacked American Airlines flight slammed into the building on Sept. 11. The terrorist attack caused extensive damage to the west face of the building and followed similar attacks on the twin towers of the World Trade Center in New York City.