From reports I have seen, a mass shooting where there is no armed resistance they average ten casualties. When there is armed resistance they average three!
One thing would help reduce these mass shooting would be to deny the shooter his T V moment in the sun. The nut in New Zealand live streamed his atrocity. I know that asking the media to do something responsibly is a tall order. If they would report the event but never film or name the perp it would rob him of the fame he seeks and to a large portion, the reason! Each of these nuts try to come up with some more horrible than the last to get more air time.
What proves this is that when a T V station, radio station or newspaper recieves a threat they never, never report it because it incites copycats!