California Gov. Jerry Brown has rejected parole for a man convicted of gunning down a San Diego police officer in 1978 when he was a 17-year-old gang member.

Brown's decision late Friday rejected the recommendation in August of a state parole board, which called for the release of Jesus Cecena (suh-SAY-nuh).

Brown says he acknowledges Cecena was a minor when the crime was committed and that he has worked to improve himself while in prison.

But Brown says the seriousness of the crime combined with Cecena's minimizing of it forces him to refuse. Brown reversed a previous parole recommendation for Cecena in 2014.

Cecena was tried as an adult and sentenced to life in prison without the possibility of parole for shooting 30-year-old Officer Archie Buggs four times during a vehicle stop in November 1978. The term was later modified, giving him a chance at parole.