** FILE ** Under heavy guard: The Washington Navy Yard was closed to all but essential personnel on Tuesday, Sept. 17, 2013, the day after a gunman launched an attack that hit office workers in the cafeteria and in the hallways at the military installation. (Associated Press)

** FILE ** Under heavy guard: The Washington Navy Yard was closed to all but essential personnel on Tuesday, Sept. 17, 2013, the day after a gunman launched an attack that hit office workers in the cafeteria and in the hallways at the military installation. (Associated Press)