America Marks 15th Anniversary of 9/11 Terror Attacks

Firefighters perform the changing of the guard at the FDNY Memorial Wall near the World Trade Center on Sept. 11, 2016.

A man holds a sign as he attends the ceremony for the victims of the terrorist attacks at the National September 11 Memorial and Museum.

A man places a paper into the 9/11 memorial names during the anniversary memorial service in New York.

Firefighters arrive for a memorial service at the World Trade Center complex.

Ann McGuire pays her respects at the Steel Beam Memorial in Jacksonville, North Carolina.

A firefighter stands as part of an honor guard at the FDNY Memorial Wall.

New York Yankees pitcher Dellin Betances, left, and manager Joe Girardi carry a wreath to the September 11th memorial in Monument Park at Yankee Stadium.

President Barack Obama sits onstage before delivering remarks at an observance ceremony at the Pentagon.

Firefighters hold out a flag during the commemoration ceremony at the National September 11 Memorial and Museum.

A flag stands amid names on the 9/11 memorial before the start of the anniversary memorial service to 9/11 victims in New York.

A girl holds her mother during a commemoration ceremony for the victims at the National September 11 Memorial and Museum.

People attend a commemoration ceremony at the National September 11 Memorial and Museum.

A man ties a memorial ribbon to the exterior wall of St. Paul's Chapel In Manhattan, New York.

Police officers stand outside Ground Zero.

FULL COVERAGE: Remembering 9/11