U.S. Airmen with the Laughlin Air Force Base honor guard ceremoniously fold the installation flag during a Sept. 11 remembrance retreat ceremony at the base in Texas Sept. 11, 2014. 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. (U.S. Air Force photo by Staff Sgt. Steven R. Doty/Released)