Serious issue - Help!

What is the name of your state (only U.S. law)? MI

I am posting this for my dad. He kicked out my half-brother who is 21 because he just wasn't doing anything with his life. Well my dad was cleaning out my half-brother's room and found a loaded .38 revolver (unregistered and unlicensed).

What would be the best way to go about this while getting my half-brother in as little trouble as possible?

--Edit--
I just realized I posted this in the wrong section, I apologize for that. For some reason the mentality of having a half-brother made me put it in the 'Juvenile' section.+

He can contact the police department, explain the situation, and ask how to get it rectified.

Call the cops. They can check to see if it was stolen etc... If not they can take it if your dad does not want to keep it.