A U.S. civilian contractor plays "Amazing Grace" during a 9/11 remembrance ceremony Sept. 11, 2014, at Kandahar Airfield, Afghanistan. It was the 13-year anniversary of the terrorist attacks. Terrorists hijacked four passenger aircraft Sept. 11, 2001. Two of the aircraft were deliberately crashed into the World Trade Center in New York; one was crashed into the Pentagon; the fourth crashed near Shanksville, Pa. Nearly 3,000 people died in the attacks.