Remembering Sept. 11

A man at a commemoration ceremony in New York holds a sign remembering a woman killed during the terrorist attack on the World Trade Center on Sept. 11, 2001.

A young girl holds onto her mother during a commemoration ceremony for the victims of the terrorist attacks at the National September 11 Memorial and Museum in New York.

Family members and friends, many holding signs commemorating their loved ones killed in the terrorist attacks, attend a ceremony at the National September 11 Memorial in New York.

A ceremony is held to honor Sept. 11 victims at the site of the attack in lower Manhattan.

A visitor pays tribute to the passengers and crew at the Flight 93 National Memorial in Shanksville, Pa., on Sunday as the nation marks the 15th anniversary of the Sept. 11 attacks.