While this is all very amusing , responding to calls for help from behind a locked residential door that may or may not be legitimate is quite different from being in a public place and WATCHING some nut case mowing people down with a gun . Also I don't think anyone inside of a large enclosed Mall would wonder if the loud bangs they were hearing were a car backfiring rather than gun shots , especially if they were accompanied by screams from several people for help as they ran away from the vicinity of the bangs .