Thats good then they can kill each other. Most criminals are cowards. They choose criminal life because they are too lazy to do anything else or were pushed into it without a choice. Most of their lives end up badly or they find Jesus and pretend that they were forgiven. But they will get whats deserved in the end. Every action has an equal and opposite reaction. Newton's Third Law of Motion

There need to be more checks to see if you have the mental health to own a gun. Nothing can really stop the black market guns, but it needs to be harder for the crazies to get a legal gun.