U.S. Air Force Staff Sgt. Jonathan Horton, 633rd Security Forces Squadron unit trainer, simulates being shot during an active-shooter exercise at Langley Air Force Base, Va., Nov. 19, 2013. Horton portrayed an Airman stricken with post-traumatic stress disorder and took hostages into a dormitory day room, making demands and threatening to kill his captives before being taken down by 633rd SFS first responders. (U.S. Air Force photo by Airman 1st Class Kimberly Nagle/Released)