Firefighters hose down the debris of World Trade Center's Building 7, Wednesday, Sept. 12, 2001, as fire continued to burn in part of the complex that collapsed with the twin towers in Tuesday's terrorist attack. The building was their third in the World Trade Center building to collapse. (AP Photo/Beth Keiser)

A Fox TV broadcast shows an airliner creating a ball of fire as it impacts one of the towers of the World Trade Center, September 11, 2001. All of the Big Four networks canceled their entire lineups of daytime, prime-time and late-night programs for the day to join cable news outlets in televising round-the-clock reports on the tragedy. (courtesy of Fox News via Reuters)

Hundreds of rescuers and emergency workers swarm all over the wreckage of the World Trade Center Towers, in New York September 12, 2001 as they search for trapped survivors of the terrorist attack on the New York landmark. Two hijacked commercial airliners were deliberately crashed into the twin towers, bringing them crashing to the ground September 11. REUTERS/Jim Bourg

Flags of member states of the European Union fly at half mast in front of the building of the European Parliament in Strasbourg September 12, 2001, following the terrorist attacks in the United States. Thousands of lives were lost September 11 after two hijacked planes plowed into the World Trade center, another plane plunged into the Pentagon and a fourth crashed in rural Pensylvania. REUTERS/Vincent Kessler

A group of firefighters work to put out fires in what is left of the destroyed World Trade Center in New York on September 11, 2001. Two hijacked U.S. commercial planes slammed into the twin towers of the World Trade Center early on Tuesday, causing both 110-story landmarks to collapse in thunderous clouds of fire and smoke. REUTERS/Shannon Stapleton

A fireball explodes from one of the World Trade Center towers after a jet airliner crashed into the building Tuesday, Sept. 11, 2001, in New York. (AP Photo/Carmen Taylor)

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)

World Trade Center tower two falls to the ground, early September 11, 2001. Both towers have fallen after planes crashed into the buildings. (Jeff Christensen/Reuters)

A group of firefighters walk amid rubble near the base of the destroyed South World Trade Center in New York on September 11, 2001. In the worst terror attack on the U.S. mainland in modern history, two hijacked planes slammed into the Trade Center's twin towers where about 40,000 people work. Both 110 story buildings collapsed within an hour of being hit. (Peter Morgan/Reuters)

The World Trade Center tower two falls to the ground after both towers were struck by airplanes September 11, 2001. The two enormous edifices both fell in a huge cloud of smoke and fire two hours after the initial impacts. (Jeff Christensen/Reuters)