It's hard to theorize based on such infrequent events, but the vast majority of these happen in official "gun free" zones (only recent exception is the Congress

It's hard to theorize based on such infrequent events, but the vast majority of these happen in official "gun free" zones (only recent exception is the Congresswoman shooting), and the killer kills himself at the first sign of lethal resistance. Of course, if this just results in displacement to other "gun free" zones, then at net there will be just as many mass shootings.