Photo gallery: September 11, 2001

A person jumps from the north tower of the World Trade Center in New York as another clings to the outside, left, while smoke and fire billow from the building on Sept. 11, 2001.

The twin towers of New York City’s World Trade Center burn after two jetliners piloted by terrorists slammed into them on Sept. 11, 2001

The south tower of the World Trade Center begins to collapse after a terrorist attack on the New York landmark on Sept. 11, 2001.

President George W. Bush‘s chief of staff, Andy Card, whispers into the president’s ear about the planes crashing into the World Trade Center as Bush was visiting Booker Elementary School in Sarasota, Fla., on Sept. 11, 2001.

A man covers his mouth to filter the air as he walks through debris after the collapse of one of New York’s World Trade Center towers on Sept. 11, 2001.

A firefighter breaks down after the World Trade Center buildings collapsed after two hijacked airplanes slammed into the twin towers in a terrorist attack on Sept. 11, 2001.

People flee the scene near New York’s World Trade Center after terrorists crashed two planes into the twin towers on Sept. 11, 2001.

Horrified bystanders in front of New York’s St. Patrick’s Cathedral look down Fifth Avenue toward the World Trade Center towers after planes crashed into their upper floors.

Two women hold each other as they watch the World Trade Center burn after a terrorist attack on the twin skyscrapers in New York on Sept. 11, 2001.

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

Pedestrians can be seen crossing the Brooklyn Bridge as they flee Manhattan after the collapse of the first World Trade Center tower.   (Doug Kanter, AFP/Getty Images)

Firefighters and emergency personnel look through the debris of United Airlines Flight 93 after it crashed on the morning of Sept. 11, 2001 near Shanksville, Pa. 40 victims were killed in the crash after passengers reportedly stormed the cockpit to thwart terrorists’ plans to use that plane as a weapon like the others.   (David Maxwell, AFP/Getty)