I’ve said it in the past, and I’ll say it again: If you want to decrease actual crime, particularly mass murders, you’ve got to raise the cost. You need to raise the cost high enough that almost no one decides it’s worth the trouble, since they’ll not get what they want out of it anyway.
You can’t do that with “laws“; bad guys never believe they are going to get caught. The most effective way to raise the cost of being a bad guy, in a way the bad guys will actually understand, is to make it more likely they’ll die during their attack– before they accomplish their goal of killing others.
You do that by doing everything you can to encourage everyone– and I mean EVERYONE– to be armed and prepared to stop an attacker in his tracks wherever one strikes. Yes, that means you will have to ignore counterfeit “laws”. Or you can try to force the anti-liberty bigots to abolish their anti-gun “laws”, but good luck with that.