Ask the police department (not by calling 911, but through a non-emergency number or by going into the station in person) if they would regard him as a trespasser under the circumstances. If they will not, and regard him as a legitimate occupant due to the length of his residence, proceed to evict him.
A three-day notice is for nonpayment of rent, and he has never had to pay rent (so his rent is not late). Here's a guide to California eviction.

