Acts of violence executed without warning by previously obscure assailants who exhibited no discernable warning signs are a global threat. These attacks are not precise tactical plans executed by highly trained military teams against worthy adversaries; rather, they are indiscriminate attacks on unsuspecting civilians who are enjoying special events or are on routine visits to places they feel safe. The results of these violent events are all too familiar: screams from the innocent who have been battered by speeding vehicles, torn apart by indiscriminate bullets, or eviscerated by shrapnel.