The charges that they are facing involuntary manslaughter means that there was no premeditation. Less than half of states have anything on the books when it comes to requiring safe storage. The strictest one is in massachusetts, where you're required to have your gun locked whenever it's stored. There's places like in california where a parent could be arrested for having a gun that a child could access in the home but that would require going and kind of knocking on doors with search warrants which just isn't done. In michigan, there's no law requiring safestorage.