U.S. service members salute as President Barack Obama lays a wreath Sept. 11, 2013, during a remembrance ceremony at the Pentagon to honor the victims of the attacks on the Pentagon Sept. 11, 2001. The president joined Secretary of Defense Chuck Hagel and Chairman of the Joint Chiefs of Staff Army Gen. Martin Dempsey along with family members of those killed 12 years ago. 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.