North Tower Smoke

The north tower of the World Trade Center collapses after being struck by hijacked American Airlines Flight. 11, Tuesday, Sept. 11, 2001. (AP Photo Richard Drew)

Burning Tower

Debris falls from a burning tower (Credit: Richard Drew/AP)

Police Officers Look Up At Towers

Smoke fumes from the burning twin towers of the World Trade Center after hijacked planes crashed into them on September 11, 2001. (AP Photo/Richard Drew)

Falling Man

A person falls headfirst from the north tower of the World Trade Center. (AP Photo/Richard Drew)

Firemen Debris

Firemen gather on a debris-covered street after the collapse of the twin towers of the World Trade Center on September 11, 2001.(AP Photo/Richard Drew)

Firemen Covered In Dust

Firemen gather on a debris-covered street after the collapse of the twin towers of the World Trade Center on September 11, 2001. (credit: AP Photo/Richard Drew)

George Pataki, Rudy Giuliani and Hillary Clinton

Gov. George Pataki, Mayor Rudolph Giuliani and Sen. Hillary Clinton tour the WTC site on Wednesday, Sept. 12, 2001. (credit: Robert F. Bukaty/AP)

Marcy Borders

Marcy Borders is covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed. Borders was caught outside on the street as the cloud of smoke and dust enveloped the area. (Credit: Stan Honda/AFP/Getty Images)

South Tower Collapse

The south tower of the World Trade Center collapses Tuesday Sept. 11, 2001. (AP Photo/Richard Drew)

North Tower Before Collapse

This is the north tower of the World Trade Center 30 seconds before its collapse. (AP Photo/Richard Drew)

Man Walks Through Rubble

A man with a fire extinguisher walks through rubble after the collapse of the first World Trade Center Tower (Credit: Doug Kanter/AFP/Getty Images)

NYPD police officer Ken Radigan

NYPD police officer Ken Radigan rubs his eyes after briefly sleeping in a pew at St. Paul's Episcopal Chapel, near the site of the World Trade Center attack, September 21, 2001. The chapel served as a relief area for rescue workers. (Photo by Mario Tama/Getty Images)

Plane Heads Into Tower

United Airlines Flight 175 nears the South Tower of the World Trade, which it struck at 9:03 a.m. (Credit: AP Photo/Carmen Taylor)

People Fleeing

People seen fleeing as the World Trade Center towers collapse (Credit: Suzanne Plunkett/AP)

What's Left Of the Twin Towers

What's Left Of the Towers (Credit: Graham Morrison/AP)

Smoke Behind Lady Liberty

Thick smoke billows into the sky from the area behind the Statue of Liberty where the World Trade Center towers once stood. (Credit: Daniel Hulshizer/AP)

President Bush With Firefighter

President George W. Bush stands next to retired firefighter Bob Beckwith, as he speaks to volunteers and firemen after surveying the damage at the site of the World Trade Center on Sept 14, 2001. (Credit: Paul J. Richards/AFP/Getty Images)

Bush Told About Attacks

This Sept. 11, 2001 photo from an early morning school reading event in Sarasota, Florida, shows White house Chief of Staff Andrew Card informing President George W. Bush of the attacks on the World Trade Center. (Credit: Paul J. Richards/AFP/Getty Images)

Ground Zero

New York City firefighters look at the destroyed facade of the World Trade Center September 13, 2001 two days after the twin towers were destroyed when hit by two hijacked passenger jets. (Photo by Chris Hondros/Getty Images)

Firefighter Walks Away From Towers

An unidentified New York City firefighter walks away from Ground Zero after the collapse of the Twin Towers September 11, 2001. (Photo by Anthony Correia/Getty Images)

World Trade Center Attacked

Hijacked United Airlines Flight 175 from Boston crashes into the south tower of the World Trade Center and explodes at 9:03 a.m. on September 11, 2001. (Photo by Spencer Platt/Getty Images)

Rescue Workers Survey Damage

Rescue workers survey damage to the World Trade Center September 11, 2001. (Credit: Doug Kanter/AFP/Getty Images)

NYC Firefighter Calls For Help

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 Jim Watson/Getty Images)

Edward Fine

This photo shows Edward Fine covering his mouth as he walks through the debris after the collapse of one of the World Trade Center Towers on 9/11/01. Fine was on the 78th floor of 1 World Trade Center when it was hit by a hijacked plane. (Credit: Stan Honda/AFP/Getty Images)

Man Cries

People run away as the North Tower of World Trade Center collapses after a hijacked airliner hit the building September 11, 2001. (Photo by Jose Jimenez/Primera Hora/Getty Images)