9/11/2001

A jet airliner hijacked by terrorists is lined up to strike one of the World Trade Center towers on Sept. 11, 2001, in Manhattan.

As the north tower of the World Trade Center burns after being struck by hijacked American Airlines Flight 11, hijacked United Airlines Flight 175 nears the south tower of the World Trade Center on Sept, 11, 2001.

An explosion rips through the south tower of the World Trade Center in Manhattan after terrorists in the hijacked United Airlines Flight 175, which departed from Boston en route for Los Angeles, crashed into it Sept. 11, 2001. The north tower is seen burning after American Airlines Flight 11 crashed into the tower at 8:45 a.m.

A fireball explodes from one of the World Trade Center towers after a hijacked airliner crashed into the building on Sept. 11, 2001, in Manhattan.

Rose Parascandola of Brooklyn flees the Twin Towers of the World Trade Center, which was engulfed in flames after being struck Sept. 11, 2001, by terrorists aboard hijacked airliners. The building collapsed a short time later.

The north tower of the World Trade Center goes up in flames after a plane struck the building on Sept. 11, 2001.

The burning World Trade Center is seen from Brooklyn. (Sept. 11, 2001)

The Twin Towers of the World Trade Center in lower Manhattan are seen burning behind the Empire State Building on Sept. 11, 2001.

In this photo taken by the NYPD and provided by ABC News, smoke and ash engulf the general area of the World Trade Center in Manhattan after terrorists crashed airplanes into the site. (Sept. 11, 2001)

In this photo taken by the NYPD and provided by ABC News, smoke and ash engulf the general area of the World Trade Center in Manhattan after terrorists crashed airplanes into the towers. (Sept. 11, 2001)

People make their way amid debris from the World Trade Center in Manhattan on 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.

Firefighter Armondo Reno screams in pain during his rescue shortly after both towers of Manhattan's World Trade Center collapsed following the terrorist attacks on Sept. 11, 2001.

The Rev. Raymond Nobiletti from the Church of the Transfiguration helps people flee the area after policemen shouted at them to run as the south tower of the World Trade Center collapsed on Sept. 11, 2001.

Edward Fine covers his mouth as he walks through the debris after the collapse of one of the World Trade Center towers on Sept. 11, 2001, in Manhattan. Fine was on the 78th floor of 1 World Trade Center when it was hit by a hijacked plane. A photo of him emerging from the debris of the attack appeared on the cover of Fortune magazine and he contacted the magazine to identify himself.

Julie McDermott, center, walks with other victims as they make their way through debris near the World Trade Center in Manhattan on Sept. 11, 2001. Earlier in the day terrorists crashed two airliners into the buildings, bringing down the twin 110-story towers.

People walk away from the World Trade Center site in Manhattan early on Sept. 11, 2001, after both towers were hit by terrorists who hijacked airliners.

Emergency personnel look for victims and fight fires in the ruins of the World Trade Center on Sept. 11, 2001, after a terrorist attack leveled both buildings in Manhattan.

Firefighters make their way through the rubble on Sept. 11, 2001, after terrorists crashed two hijacked airliners into the World Trade Center in a deadly series of blows that brought down the twin 110-story towers in Manhattan.

An emergency worker is assisted in lower Manhattan on Sept. 11, 2001, after the terrorist attacks on the World Trade Center.

A street scene aftermath of the World Center attack on Tuesday Sept. 11, 2001.

The view looking south on West Street toward the World Trade Center on Sept. 11, 2001.

The remains of the World Trade Center stands amid the debris following the terrorist attack on the building in New York, Tuesday, Sept. 11, 2001. (AP Photo/Alex Fuchs)

Firefighters raise a flag late in the afternoon on Sept. 11, 2001, in the wreckage of the World Trade Center towers in Manhattan after the terrorist attacks that morning.

A firefighter pauses on a bench as he works in lower Manhattan at the scene of the World Trade Center terrorist attacks on Sept. 11, 2001.

A helicopter flies over the Pentagon in Washington on Sept. 11, 2001, as smoke billows from the building. The Pentagon took a direct hit from an aircraft hijacked by terrorists.

Flames and smoke pour from a building at the Pentagon on Sept. 11, 2001, in Washington after a direct, devastating hit from an aircraft hijacked by terrorists.

Fires burn amid the rubble outside the Pentagon on Sept. 11, 2001, after the building took a direct, devastating hit from an aircraft hijacked by terrorists.

A Pentagon employee is aided outside the building on Sept. 11, 2001, after the building took a direct, devastating hit from an aircraft in a terrorist attack.

Vehicles travel on Interstate 395, leaving Washington, in front of the Pentagon, after an airliner hijacked by terrorists crashed into the building on Sept. 11, 2001.

Firefighters and emergency personnel investigate the scene of the crash in Shanksville, Pa., of a United Airlines Flight 93, which was hijacked by terrorists on Sept. 11, 2001. Radar showed the San Francisco-bound airplane from Newark, N.J., had nearly reached Cleveland when it made a sharp left turn and headed back toward Pennsylvania, crashing in a grassy field edged by woods about 80 miles southeast of Pittsburgh. Everyone onboard the plane was killed.

An FBI aerial photograph, taken Wednesday, Sept. 12, 2001, shows the crash site of hijacked United Airlines Flight 93 in Shanksville, Pa. The Boeing 757 was headed from Newark, N.J., to San Francisco when it made an abrupt turn near Cleveland and veered back east across Pennsylvania before crashing in Shanksville, killing all 44 aboard. Flight 93 was the fourth plane to crash in a coordinated terrorist attack that included Manhattan's World Trade Center and the Pentagon, and the only one that didn't take lives on the ground.

Investigators and police probe the site where a jet crashed Sept. 11, 2001, near Shanksville, Pa. A passenger on United Airlines Flight 93 called from his cell phone from a locked bathroom and delivered a chilling message: "We are being hijacked, we are being hijacked!'' Minutes later the jetliner crashed in western Pennsylvania with 45 people aboard, the last of four closely timed terror attacks that day across the country.

Emergency workers look at the crater created when United Airlines Flight 93, hijacked by terrorists, crashed near Shanksville, Pa., on Sept. 11, 2001.

A screen at the American Airlines terminal at Los Angeles International Airport shows that all flights have been canceled as the airport is shut down on Sept. 11, 2001. Flights were canceled nationwide after planes hijacked by terrorists crashed in three places in the United States: the World Trade Center in Manhattan, the Pentagon in Washington, D.C., and in Shanksville, Pa.