Smoke raises from New York City shortly after the collapse of the World Trade Centers, Tuesday, Sept. 11, 2001.

Smoke raises from where the World Trade Centers once stood in New York City at sunset on Tuesday, Sept. 11, 2001.

Firefighters pour water on the rubble that was the World Trade Center in New York, Tuesday, Oct. 2, 2001. Three weeks after the attack fires continue to burn in the rubble.

Firefighters pour water on the rubble that was the World Trade Center in New York, Tuesday, Oct. 2, 2001. Three weeks after the attack fires continue to burn in the rubble. (AP Photo/Ed Betz)

Five weeks after the World Trade Center attacks, firefighters pour water on the rubble in New York, Tuesday, Oct. 16, 2001. (AP Photo/Ed Betz)

Workers cut away part of the facade of the World Trade Center in New York, at sunrise Monday, Oct. 15, 2001. (AP Photo/Ed Betz)

Excavators work to clear debris from site of the World Trade Center attacks in New York, Friday, Oct. 19, 2001. (AP Photo/Ed Betz)

Water sprayed by a firefighter creates a rainbow at the scene of the World Trade Center in New York, Tuesday, Oct. 16, 2001. (AP Photo/Ed Betz)

A worker suspended from a crane examines a remaining wall of the South Tower of the World Trade Center in New York, Friday, Oct. 19, 2001. (AP Photo/Ed Betz)

Workers suspended from a crane cut away part of the remaining wall of the South Tower of the World Trade Center in New York, Friday, Oct. 19, 2001. (AP Photo/Ed Betz)

Smoke continues to rise from the rubble of the World Trade Center in New York, Monday, Oct. 15, 2001. (AP Photo/Ed Betz)

A worker stands on top of a piece of heavy equipment as clean up work continues at the site of the World Trade Center attacks in New York, Sunday, Oct. 21, 2001. (AP Photo/Ed Betz)

Workers are suspended from a crane in front of the remains of the North Tower of the World Trade Center in New York, Monday, Oct. 15, 2001. (AP Photo/Ed Betz)

The Empire State Building remains lit red white and blue at daybreak as work continues at the World Trade Center in New York, Monday, Oct. 15, 2001. (AP Photo/Ed Betz)

Firefighters and rescue workers look throught the rubble of the World Trade Center in New York, Monday, Oct. 15, 2001. (AP Photo/Ed Betz)

Firefighters dig through the rubble of the World Trade Center in New York, Tuesday, Oct. 16, 2001. (AP Photo/Ed Betz)

Workers clean the side of One Liberty Plaza, located across the street from the World Trade Center in New York, Tuesday, Oct. 16, 2001. The building which was damaged by the collapse of the World Trade Center, remains covered with a red mesh protective covering. (AP Photo/Ed Betz)

Workers suspended from a crane inspect a remaining wall of the south tower of the World Trade Center in New York, Friday, Oct. 5, 2001. (AP Photo/Ed Betz)

Firefighters look on as a large section of the outer structure of the World Trade Center is removed in New York, Tuesday, Oct. 16, 2001. (AP Photo/Ed Betz)

Workers suspended from a crane cut away part of the remaining wall of the South Tower of the World Trade Center in New York, Friday, Oct. 19, 2001. (AP Photo/Ed Betz)

Workers look up at a large illuminated cross near the rubble that was the World Trade Center in New York, Tuesday, Oct. 3, 2001. (AP Photo/Ed Betz)

Firefighters and police watch as an excavator spreads out a pile of rubble so it can be searched at the site of the World Trade Center attacks in New York, Friday, Oct. 19, 2001. (AP Photo/Ed Betz)

Firefighters carry a flag drapped body out of the rubble that was once the World Trade Center in New York, Sunday, Oct. 21, 2001. (AP Photo/Ed Betz)

Firefighters, police officers and rescue workers salute as a flag drapped body is removed from the site of the World Trade Center attacks in New York, Sunday, Oct. 21, 2001. (AP Photo/Ed Betz)

Firefighters, police officers and rescue workers gather around three flag draped bodies at the site of the World Trade Center attacks in New York, Sunday, Oct. 21, 2001. (AP Photo/Ed Betz)

Rescue workers form a circle and join a chaplin as he prays over remains that were removed from the rubble of what was once the World Trade Centers in New York, Thursday, Sept. 27, 2001.

Firefighters place a flag drapped body into an ambulance at the site of the World Trade Center attacks in New York, Tuesday, Oct. 30, 2001. (AP Photo/Ed Betz)

Firefighters and rescue workers seen through a crane salute as a flag draped body is removed from the rubble at the site of the World Trade Center attacks in New York, Friday, Nov. 9, 2001. (AP Photo/Ed Betz)

Firefighters and police look on as a flag draped body is removed from the site of the World Trade Center terrorist attacks in New York, Friday, Dec. 7, 2001. (AP Photo/Ed Betz)

A worker removes his helmet as firefighters carry a body from the site of the World Trade Center terrorist attacks in New York, Friday, Dec. 7, 2001. (AP Photo/Ed Betz)

Firefighters salute as a flag draped body is removed from the site of the World Trade Center terrorist attacks in New York, Friday, Dec. 7, 2001. (AP Photo/Ed Betz)

Workers suspended from a crane inspect a remaining wall of the south tower of the World Trade Center in New York, Friday, Oct. 5, 2001. (AP Photo/Ed Betz)

Firefighters search thru the rubble at the site of the World Trade Center in New York, Friday, Oct. 5, 2001.

Firefighters and rescue workers look thru rubble on a roof of the World Financial Center located across the street from the area where the World Trade Center once stood in New York, Thursday, Sept. 27, 2001. (AP Photo/Ed Betz)

Police Officers overlook the area where the World Trade Center once stood in New York, Thursday, Sept. 27, 2001. (AP Photo/Ed Betz)

Workers tie a large American flag on to the side of a building on a few blocks from the site where the World Trade Centers once stood in New York, Monday, Sept. 24, 2001. (AP Photo/Ed Betz)

Smoke continues to rise from the scene of the World Trade Center in New York, Tuesday, Oct. 9, 2001. Four weeks after two planes crashed into the buildings, firefighters continue to pour water on smoke rising from the ground. (AP Photo/Ed Betz)

Firefighters salute as flaged draped remains are removed fron the rubble of the World Trade Center in New York, Tuesday, Oct. 9, 2001.