You can file another police report. And call the DA's office and demand prosecution. However, if he has come and gone from the home in the past, or has a key, or you've declined to prosecute before, the DA's office may decline to prosecute. If you report the stolen gun, the police to get a little more interested in prosecuting.
In any event you should make it very clear to the step son that he is not to come into the home without you or your wife being present. A letter, perhaps delivered to him personally by a third non related party may be enough so that next time this happens, the police will feel they have enough evidence to prove he was trespassing in the home. The letter will have to be signed by both you and your wife, since she has equal rights to possession of the home and even if you want him to never come over, she can still allow it.
You might also try changing the locks.
This comment is general in nature and is not intended as legal advice. It does not create an attorney client relationship and obviously is not confidential. You should contact an attorney in your area who can review with you all of the relevant facts and give you specific legal advice.
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