Who's responsible for previous fines on used car?

I'm going to re-word this differently cuz I think I was misunderstood. My friend just bought a used car and the current owner still has his plates on the car and we just found out he had the car uninsured for about a month. Is this going to be a problem to now register the car in my friend's name? Is my friend going to be be responsible for any previous fees on the car? Should the owner return the plates to the DMV or should my friend do it when he goes to register the car? The title is signed and in possession.