SACRAMENTO (AP) — California Gov. Jerry Brown has rejected parole for a man convicted of killing a San Diego police officer during a 1978 traffic stop.

Brown’s decision late Friday rejected the recommendation in August of a state parole board, which called for the release of 54-year-old Jesus Salvador Cecena.

Cecena, who was a 17-year-old gang member at the time of the shooting, was tried as an adult and sentenced to life in prison without the possibility of parole for shooting San Diego Officer Archie Buggs, 30, four times.

The governor said in his written rejection that he acknowledges Cecena was a minor when the crime was committed and that he has worked to improve himself during in prison and avoided serious misconduct for decades.

But Brown said negative factors outweigh those considerations.

“Mr. Cecena turned a routine stop for speeding into a cold-blooded execution of a beloved police officer who worked earnestly to protect his community,” Brown wrote in his decision.

Brown also said Cecena has yet to provide a credible explanation for the crime or sufficiently explore his motives, and that he still minimizes the crime.

“I am troubled that Mr. Cecena continues to whitewash the murder of Officer Buggs,” Brown wrote. The governor cited an interview last year with a psychologist where Cecena said he killed the officer in a panic when evidence showed he aimed carefully.

His term was later modified, giving him a chance at parole under a state law that allows youth offenders serving life without the possibility of parole to petition for release once they have served at least 15 years.

Cecena was also recommended for parole in 2014, but Brown reversed that decision too.