An American flag flies near the base of the destroyed World Trade Center in New York, Sept. 11, 2001.

The wreck of the World Trade Center smolders in the background as a man runs in New York, Sept. 11, 2001.

The second tower of the World Trade Center explodes after being hit by a hijacked airplane in New York, Sept. 11, 2001.

A rescue helicopter surveys damage as firefighters battle flames after an airplane crashed into the Pentagon outside of Washington, Sept. 11, 2001.

People run from the collapse of World Trade Center Tower in New York, Sept. 11, 2001.

People look out of the windows of the burning North tower of the World Trade Center in New York, Sept. 11, 2001.

A group of firefighters walk amid rubble near the base of the destroyed south tower of the World Trade Center in New York, Sept. 11, 2001.

The remaining tower of World Trade Center dissolves in a cloud of dust and debris about a half hour after the first twin tower collapsed in New York, Sept. 11, 2001.

With the skeleton of the World Trade Center twin towers in the background, New York City firefighters work amid debris on Cortlandt St. after the terrorist attacks, Sept. 11, 2001.

A person jumps out of burning building of World Trade Center in New York, Sept. 11, 2001.

Firemen walk through a dust and debris covered street in lower Manhattan, Sept. 11, 2001, after a terrorist attack at the World Trade Center.

People flee lower Manhattan across the Brooklyn Bridge in New York, Sept. 11, 2001, following a terrorist attack on the World Trade Center.

People flee the falling South Tower of the World Trade Center, September 11, 2001.