U.S. Air Force Staff Sgt. Roger Wood, a trainer with the 633rd Security Forces Squadron, acts as an active shooter at Langley Air Force Base, Va., Nov. 19, 2015. The profile of an active shooter includes an individual actively engaged or attempting to kill people in a confined and populated area, in most cases there is no pattern or method to their selection of victims. (U.S. Air Force photo illustration by Staff Sgt. Ciara Gosier)