You are dreaming. You can have the penalty be life in prison and it will no effect on inner city violence or mass killings.
I disagree, it would have a very significant impact on inner city violence. Perpetrators would either already be in jail or would fear getting caught with a gun if there were zero tolerance. Non-urban mass killings is a tougher nut to crack but it's a tiny percentage of gun deaths. It needs to involve mental health professionals working with lawmakers to make new policies, I just don't know what the solution is to that...