Sirhan Sirhan, who assassinated presidential candidate Robert F Kennedy in 1968, is asking a judge to free him from prison by reversing a decision by the California governor to deny him parole.

Sirhan shot Kennedy in 1968 at the Ambassador hotel in Los Angeles, moments after the US senator from New York claimed victory in California’s pivotal Democratic presidential primary. He wounded five others during the shooting.

Gavin Newsom, the California governor, in January overruled two parole commissioners who had found that Sirhan no longer was a risk. The governor argued Sirhan remains a threat to the public and has not taken responsibility for a crime that changed American history.

But Sirhan Sirhan’s attorney, Angela Berry, says there is no evidence her now 78-year-old client remains dangerous.

She is filing what is known as a writ of habeas corpus asking a judge to rule that Newsom violated state law, which holds that inmates should be paroled unless they pose a current unreasonable public safety risk. Recent California laws also required the parole panel to consider that Sirhan committed the offense at a young age, when he was 24, and that he is now an elderly prisoner.

Berry said she was challenging the governor’s reversal as an “abuse of discretion”, a denial of Sirhan’s constitutional right to due process and as a violation of California law. It also alleges that Newsom misstated the facts in his decision.

Berry said the governor “acted with personal bias, incorporated the wrong law, ignored mitigation evidence, and did not afford Sirhan the same rights as others eligible for parole”.

In a recorded statement played by his attorneys, Sirhan said he was hopeful the courts would issue an “unbiased and apolitical decision” based on his achievements behind bars, including self-help programming, a college education, mentoring incarcerated people and facing no disciplinary write-ups for nearly a half century.

“All I want to do is return home to my brother and live out the rest of our days in peace,” he said. “The remorse I carry for my actions is something I live with each day. To transform this weight into something positive, I have dedicated my life to self improvement and mentoring others in prison on how to live a peaceful life that revolves around non-violence.”

Sirhan said he had been in contact with the victims and their families over the years, “making direct and indirect amends for my actions”.

Newsom’s decision split the Kennedy family, with two of Kennedy’s sons, Douglas Kennedy and Robert F Kennedy Jr, supporting his release. But Kennedy’s wife, Ethel Kennedy, and six of Kennedy’s nine surviving children opposed his parole.

Sirhan noted that some Kennedy relatives have publicly said he was “worthy of forgiveness and deserving of freedom”, adding, “I’m humbled by their love and empathy.”

Newsom has cited Robert F Kennedy as his political hero and keeps Kennedy photos in both his official and home offices, including one of Kennedy with his late father. Berry accused him of politicizing the parole process and putting his “political goals and agenda above that of the constitution”.

Newsom’s office did not respond to a request for comment.

It is unclear how quickly a judge might rule on Berry’s petition, and either side could appeal an adverse decision, but Sirhan is set for a new parole hearing on 1 March.

Sirhan originally was sentenced to death, but that sentence was commuted to life when the California supreme court briefly outlawed capital punishment in 1972.

“To have an immaculate record of almost five decades is the exception, not the rule. Sirhan is the epitome of what a model prisoner is and what rehabilitation looks and sounds like,” said Jen Abreu, executive director of Redemption Row California, who has worked with Sirhan. She noted research suggesting that lengthening already long prison sentences does not deter violence and that elderly prisoners have low recidivism rates.

“The public hysteria that those who have committed murder will eventually kill again is simply unfounded.”