Lt. Col. Dave Grossman spoke with POLICE Editor David Griffith while attending the TREXPO East show and conference in Chantilly, Va. The author of "On Killing" and former Army Ranger who is also one of the nation's experts on human aggression and violent crime gave the event's keynote address. In a podcast that was recorded Wednesday, Aug. 19, Grossman discusses the warrior spirit, concealed carry, and preventing terrorism. Grossman concluded his presentation on Aug. 20.