Smoke pours from the World Trade Center after it was hit by two hijacjked passenger planes September 11, 2001 in New York City in an alleged terrorist attack. (Photo by Robert Giroux/Getty Images)

A fiery blasts rocks the World Trade Center after being hit by two planes September 11, 2001 in New York City. (Photo by Spencer Platt/Getty Images)

People watch World Trade Center burn September 11, 2001 after two hijacked airplanes slammed into the twin towers in New York City. (Photo by Spencer Platt/Getty Images)

People walk in the street in the area where the World Trade Center buildings collapsed September 11, 2001 after two airplanes slammed into the twin towers in a suspected terrorist attack. (Photo by Mario Tama/Getty Images)

People walk over the Brooklyn Bridge as the world trade center burns September 11, 2001 after two hijacked airplanes slammed into the twin towers in New York City. (Photo by Spencer Platt/Getty Images)

Civilians flee as a tower of the World Trade Center collapses September 11, 2001 after two airplanes slammed into the twin towers in an alleged terrorist attack. (Photo by Mario Tama/Getty Images)

Smoke comes out from the Southwest E-ring of the Pentagon building September 11, 2001 in Arlington, Va., after a plane crashed into the building and set off a huge explosion. (Photo by Alex Wong/Getty Images)

(PUERTO RICO OUT) Firefighters walk towards one of the tower at the World Trade Center before it collapsed after a plane hit the building September 11, 2001 in New York City. (Photo by Jose Jimenez/Primera Hora/Getty Images)

(PUERTO RICO OUT) Policemen and firemen run away from the huge dust cloud caused as the World Trade Center's Tower One collapses after terrorists crashed two hijacked planes into the twin towers, September 11, 2001 in New York City. (Photo by Jose Jimenez/Primera Hora/Getty Images)

New York City firefighters take a rest at the World Trade Center after two hijacked planes crashed into the Twin Towers September 11, 2001 in New York. (Photo by Ron Agam/Getty Images)

Guatemalan pedestrians watch on TV September 11, 2001 in Guatemala City, Guatemala the moment when a second plane commandeered by unknown hijackers slammed into New York's World Trade Center. (Photo by Andrea Nieto/Getty Images)

A New York City fireman calls for 10 more rescue workers to make their way into the rubble of the World Trade Center September 14, 2001 days after the September 11, 2001 terrorist attack. (U.S. Navy Photo by Preston Keres/Getty Images)

NEW YORK - SEPTEMBER 11, 2001: (SEPTEMBER 11 RETROSPECTIVE) Smoke pours from the twin towers of the World Trade Center after they were hit by two hijacked airliners in a terrorist attack September 11, 2001 in New York City. (Photo by Robert Giroux/Getty Images)

NEW YORK - SEPTEMBER 13, 2001: (SEPTEMBER 11 RETROSPECTIVE) Rescue workers sift through the wreckage of the World Trade Center September 13, 2001 in New York City, two days after two hijacked airplanes slammed into the twin towers, levelling them in an alleged terrorist attack. (Photo by Mario Tama/Getty Images)

NEW YORK - SEPTEMBER 11: Firefighter Gerard McGibbon, of Engine 283 in Brownsville, Brooklyn, prays after the World Trade Center buildings collapsed September 11, 2001 after two hijacked airplanes slammed into the twin towers in a terrorist attack that killed some 3,000 people. (Photo by Mario Tama/Getty Images)

NEW YORK - SEPTEMBER 15: (SEPTEMBER 11 RETROSPECTIVE) Firefighter Tony James cries while attending the funeral service for New York Fire Department Chaplain Rev. Mychal Judge, in front of the St. Francis of Assisi Church September 15, 2001 in New York City. Judge died while giving the last rites to a fireman in the collapse of the World Trade Center. The World Trade Center was destroyed after both the landmark towers were struck by two hijacked planes in a terrorist attack on September 11. (Photo by Joe Raedle/Getty Images)

NEW YORK - SEPTEMBER 11: An unidentified New York City firefighter walks away from Ground Zero after the collapse of the Twin Towers September 11, 2001 in New York City. The World Trade Center's Twin Towers and the Pentagon were attacked by terrorists using commercial airliners as missiles. (Photo by Anthony Correia/Getty Images)