Newsom decided to reverse the parole board’s decision after determining that Sirhan “currently poses an unreasonable threat to public safety,” a statement from the governor’s office said.
“The Governor reached his decision based on several factors, including Mr. Sirhan’s refusal to accept responsibility for his crime, lack of insight and accountability required to support his safe release, failure to disclaim violence committed in his name, and failure to mitigate his risk factors,” the statement said.
Newsom added that Sirhan, now 77, “remains a potent symbol of political violence.”
“He does not understand, let alone have the skills to manage, the complex risks of his self-created notoriety. He cannot be safely released from prison because he has not mitigated his risk of fomenting further political violence,” the governor wrote.
Through the review process, Newsom noted his penchant for Kennedy, telling reporters he keeps a framed photo of the former senator at the entrance of his office.
CNN has reached out to Sirhan’s attorney for comment.
Kennedy family members who opposed Sirhan’s release said in a statement they were “deeply relieved” by the governor’s decision.
“The killer’s violent act contradicted the values of openness, dialogue, and democratic change that Robert Kennedy embraced and that underlie our political system,” they said. “The offender must transform himself.”
“Because of how entwined into popular culture this murder has become, amplified by the regularity of the inmate’s attempts to be freed, our family has been forced to watch our husband and father be killed thousands of times,” they said, adding that the governor’s decision “represents the vindication of the rule of law over all who would betray it with hatred and violence.”
“We are deeply grateful for this decision, aimed at ensuring that no family nor our nation will suffer the same heart-breaking, irredeemable loss,” they added.
Sirhan — who was 24 at the time — shot Kennedy in the kitchen of the Ambassador Hotel in Los Angeles following a campaign event in which Kennedy celebrated primary victories in his run for the Democratic nomination for president in 1968.
Originally sentenced to death, Sirhan’s sentence was commuted to life in prison in 1972 after the California State Supreme Court declared the death penalty unconstitutional.
CNN’s Christina Maxouris contributed to this report.