A significant number of guns used in crimes are stolen from legal gun-owners. With legal guns less prevalent, the people you refer to would have less access to them as well. You could require better care in storage of guns, so that they can't be stolen as easily. You could increase funding for combating illegal gun trafficking. I'm not saying these are good solutions to the issue, but there are a lot of things one could do through the law to help keep guns away from criminals.