9/11: The images of the attack that changed the world

An American flag flies near the destroyed World Trade Center in New York City on Sept. 11, 2001, hours after the collapse of the towers. (REUTERS/Peter Morgan)

President George W. Bush listens as White House Chief of Staff Andrew Card informs him of a second plane hitting the World Trade Center. Bush was conducting a reading seminar at the Emma E. Booker Elementary School in Sarasota, Fla.  (REUTERS/Win McNamee)

Pedestrians react to the World Trade Center collapse Sept. 11, 2001.  (REUTERS/Stringer)

People look out of the burning North Tower of the World Trade Center in New York City on Sept. 11, 2001.  (B REUTERS/Jeff Christensen JC)

Smoke rises from the burning twin towers of the World Trade Center after hijacked planes crashed into the towers in New York City. Sept. 11, 2001.  (AP Photo/Richard Drew)

The second tower of the World Trade Center bursts into flames after being hit by a hijacked airplane in New York in this Sept. 11, 2001.  (REUTERS/Sara K. Schwittek)

Cars smoulder in the street as the destroyed World Trade Center burns in New York on Sept. 11, 2001.  (REUTERS/Peter Morgan JC/SV)

Firefighters work beneath the destroyed mullions, the vertical struts that once faced the outer walls of the World Trade Center towers, after the Sept. 11, 2001 terrorist attack. (AP Photo/Mark Lennihan)

A rescue helicopter surveys damage to the Pentagon as firefighters battle flames after a hijacked airplane crashed into the U.S. military headquarters outside of Washington, on Sept. 11, 2001.  (REUTERS/Larry Downing-Files HB)

Photo detail of one of the granite slabs and the steel from the original World Trade Center is seen at the 9/11 Memorial Glade at the National September 11 Memorial & Museum in New York.  (AP Photo/Mary Altaffer)

A rose rests next to a photograph of New York City Fire Department Lt. Steven Reisman in the 9/11 Memorial Glade near the National September 11 Memorial & Museum.   (AP Photo/Seth Wenig, File)

A person walks through the 9/11 Empty Sky Memorial in Liberty State Park as the sun sets on Oct. 24, 2018 in Jersey City, N.J.  (Gary Hershorn/Getty Images)

Norma Molina, of San Antonio, Texas, leaves flowers by the names of firefighters from Engine 33 at the September 11 Memorial. Her boyfriend Robert Edward Evans, a member of Engine 33, was killed in the north tower of the World Trade Center. (AP Photo/Mark Lennihan)

The annual Tribute in Light appears over lower Manhattan in New York City on Sept. 11, 2017 as seen from Jersey City, New Jersey. (Gary Hershorn/Getty Images)

People walk through the Empty Sky 9/11 memorial in Liberty State Park on February 27, 2018 in Jersey City, New Jersey.  (Gary Hershorn/Getty Images)