Plumes of smoke pour from the World Trade Center buildings in New York Tuesday, Sept. 11, 2001. Planes crashed into the upper floors of both World Trade Center towers minutes apart Tuesday in a horrific scene of explosions and fires that lead to the collapse of the 110-story buildings. The Empire State building is seen in the foreground. (AP Photo/Patrick Sison)

Plumes of smoke pour from the World Trade Center buildings in New York Tuesday, Sept. 11, 2001. Planes crashed into the upper floors of both World Trade Center towers minutes apart Tuesday in a horrific scene of explosions and fires that left gaping holes in the 110-story buildings. (AP Photo/Patrick Sison)

Flames and smoke pour from a building at the Pentagon Tuesday, Sept. 11, 2001, after a direct, devasting hit from an aircraft. (AP Photo/Mandatory Credit, Will Morris)

FIremen walk through a dust and debris covered street in lower Manhattan Tuesday, Sept. 11, 2001, after a terrorist attack at the World Trade Center. Two jet planes were crashed into the twin towers, collapsing them and covering the area with the debris.(AP Photo/Richard Cohen)

A jet crashes into the World Trade Center in New York, Tuesday, Sept. 11, 2001. Terrorists crashed two planes into the World Trade Center, and the twin 110-story towers collapsed Tuesday morning. (AP Photo/Moshe Bursuker)

Women wearing dust masks flee across the Brooklyn Bridge from Manhattan to Brooklyn following the collapse of both World Trade Center towers Tuesday, Sept. 11, 2001 in New York. The towers previously loomed tall in the skyline behind. (AP Photo/Mark Lennihan)

The south tower collapses as smoke billows from both towers of the World Trade Center, in New York, Tuesday, Sept. 11, 2001. In one of the most horrifying attacks ever against the United States, terrorists crashed two airliners into the World Trade Center in a deadly series of blows that brought down the twin 110-story towers. (AP Photo/Jim Collins)

Firefighters make their way through the rubble after two airliners crashed into the World Trade Center in New York Tuesday, Sept. 11, 2001. (AP Photo/Shawn Baldwin)

Firefighters make their way through the rubble after two airliners crashed into the World Trade Center in New York bringing down the landmark buildings Tuesday, Sept. 11, 2001. (AP Photo/Shawn Baldwin)

New York, UNITED STATES: TO GO WITH AFP STORY \'Americans mark 9/11 anniversary with new questions on vulnerability\' - (FILES) The twin towers of the World Trade Center billow smoke after hijacked airliners crashed into them early 11 September, 2001. Americans mark the fourth anniversary of the September 11, 2001 terror attacks Sunday nagged by new burning questions about their readiness to confront a major disaster after the debacle of Hurricane Katrina. AFP PHOTO/Henny Ray ABRAMS (Photo credit should read HENNY RAY ABRAMS/AFP/Getty Images)

A plane approaches New York\'s World Trade Center moments before it struck the tower at left, as seen from downtown Brooklyn, Tuesday, Sept. 11, 2001. In an unprecedented show of terrorist horror, the 110 story towers collapsed in a shower of rubble and dust after 2 hijacked airliners carrying scores of passengers slammed into them. (AP Photo/ William Kratzke)

A jet airliner is lined up on one of the World Trade Center towers in New York Tuesday, Sept. 11, 2001. In the most devastating terrorist onslaughts ever waged against the United States, knife-wielding hijackers crashed two airliners into the World Trade Center on Tuesday, toppling its twin 110-story towers. (AP Photo/Carmen Taylor)

Fire and smoke billows from the north tower of New York\'s World Trade Center Tuesday Sept. 11, 2001 after terrorists crashed two hijacked airliners into the World Trade Center and brought down the twin 110-story towers. (AP Photo/David Karp)

** FILE ** A person falls from the north tower of New York\'s World Trade Center as another clings to the outside, left center, while smoke and fire billow from the building, in this file photo of Tuesday Sept. 11, 2001. New York City is scheduled to release phone calls Friday, March 31, 2006 made during the attacks on Sept. 11, 2001, from 28 people trapped in the burning towers to the emergency 911 phone number. (AP Photo/Richard Drew, File)

People flee lower Manhattan across the Brooklyn Bridge in New York, Tuesday, Sept. 11, 2001, following a terrorist attack on the World Trade Center. (AP Photo/Daniel Shanken)

People flee lower Manhattan across the Brooklyn Bridge in New York, Tuesday, Sept. 11, 2001, following a terrorist attack on the World Trade Center. (AP Photo/Daniel Shanken) MANDATORY CREDIT

Police officers and civilians run away from New York\'s World Trade Center after an additional explosion rocked the buildings Tuesday morning, Sept. 11, 2001. In unprecedented show of terrorist horror, the 110-story World Trade Center towers collapsed in a shower of rubble and dust Tuesday morning after two hijacked airliners carrying scores of passengers slammed into the sides of the twin symbols of American capitalism. (AP Photo/Louis Lanzano)

** FOR USE AS DESIRED WITH SEPT. 11 ANNIVERSARY STORIES -- FILE **Smoke billows from one of the towers of the World Trade Center and flames as debris explodes from the second tower, in this Sept. 11, 2001, file photo. In one of the most horrifying attacks ever against the United States, terrorists crashed two airliners into the World Trade Center in a deadly series of blows that brought down the twin 110-story towers. This year will mark the fifth anniversary of the attacks. (AP Photo/Chao Soi Cheong/FILE)

The Statue of Liberty stands as smoke billows from the World Trade Center in New York, Tuesday, Sept 11, 2001 after terrorists crashed two hijacked airliners into the World Trade Center and brought down the twin 110-story towers. (AP Photo/Stuart Ramson)

Smoke and ash from the destroyed World Trade Center billows over the southern end of New York City\'s Manhattan as seen from Jersey City, New Jersey in the early morning, 12 September, 2001. Terrorists hijacked two commercial airliners and crashed them into each of the towers of the Trade Center. AFP Photo/Tannen Maury (Photo credit should read TANNEN MAURY/AFP/Getty Images)

Emergency personnel carry an orange body bag with the remains of a victim of the World Trade Center crash, Thursday, Sept. 13, 2001. Two hijacked airliners crashed into the towers of the World Trade Center on Tuesday, Sept. 11, destroying both buildings. (AP Photo/Bill Farrington)

Dust and debris cover the ground and cloud the air near the site of the terrorist attack on the World Trade Center in New York, Tuesday, Sept. 11, 2001. (AP Photo/Bernadette Tuazon)

People run from the collapse of one of the twin towers of New York\'s World Trade Center in this Sept. 11, 2001, file photo. (AP Photo/FILE/Suzanne Plunkett)

People run from the collapse of World Trade Center Tower Tuesday, Sept. 11, 2001 in New York. (AP Photo/Suzanne Plunkett)

People run from the collapse of World Trade Center towers in New York, Tuesday, Sept. 11, 2001 after terrorists crashed two hijacked airliners into the World Trade Center and brought down the twin 110-story towers. (AP Photo/Suzanne Plunkett)

** FOR USE AS DESIRED WITH SEPT. 11 ANNIVERSARY STORIES--FILE **People run from the collapse of World Trade Center Tower, in this Sept. 11, 2001, file photo in New York. In a horrific sequence of destruction, terrorists crashed two planes into the World Trade Center and the 110-story twin towers collapsed. This year will mark the fifth anniversary of the attacks. (AP Photo/Suzanne Plunkett/FILE)

People run from the collapse of World Trade Center Tower Tuesday, Sept. 11, 2001 in New York. In a horrific sequence of destruction, terrorists hijacked two airliners and crashed them into the World Trade Center in a coordinated series of attacks that brought down the twin 110-story towers. (AP Photo/Suzanne Plunkett)

Rubble and ash fill lower Manhattan streets after two hijacked airliners were crashed into the towers of the World Trade Center in New York, Tuesday, Sept. 11, 2001. The planes crashed into the upper floors of both World Trade Center towers minutes apart collapsing the 110-story buildings. (AP Photo/Boudicon One)

Firefighters make their way through the rubble after terrorists crashed two airliners into the World Trade Center in a deadly series of blows Tuesday that brought down the twin 110-story towers in New York Tuesday, Sept. 11, 2001. (AP Photo/Shawn Baldwin)

People make their way amid debris near the World Trade Center in New York Tuesday Sept. 11, 2001. In one of the most horrifying attacks ever against the United States, terrorists crashed two airliners into the World Trade Center in a deadly series of blows that brought down the twin 110-story towers. (AP Photo/Gulnara Samoilova)

People make their way amid debris near the World Trade Center in New York Tuesday Sept. 11, 2001. In one of the most horrifying attacks ever against the United States, terrorists crashed two airliners into the World Trade Center in a deadly series of blows that brought down the twin 110-story towers. (AP Photo/Gulnara Samoilova)

FILE - In this Sept. 11, 2001 file photo, people make their way amid debris near the World Trade Center in New York. Families of the victims of the worst terror attack on the United States in history gathered Wednesday, Sept. 11, 2013, to mark their 12th anniversary with a moment of silence and the reading of names. The Sept. 11, 2001 attacks in New York City and Washington killed almost 3,000 people and lead to a war in Afghanistan. (AP Photo/Gulnara Samoilova)

A priest aids people making their way amid debris just outside a churchyard near the World Trade Center in New York Tuesday Sept. 11, 2001. In one of the most horrifying attacks ever against the United States, terrorists crashed two airliners into the World Trade Center in a deadly series of blows that brought down the twin 110-story towers. (AP Photo/Gulnara Samoilova)

Rescue workers continue their efforts Monday, Sept. 24, 2001, at the site of the Sept. 11 World Trade Center terrorist attack in New York. (AP Photo/Ted S. Warren, Pool)