He has been essentially gagged (at least severely isolated)for 50 years. His case seemed really simple. He was an admitted ethinic Palestinian assassin, who was angry at the Kennedys for a pro Israel slant. So he pleaded guilty to get a life sentence, as opposed to the death penalty.
But then he managed to get out details that were shocking. He felt he was mind controlled and he suffered several bouts of lost memory, and he remembers nothing of killing RFK. It has been said that he never had an interest in his grandparents ancestral crib - Israel. He said his lawyer came up with the crap plea.
His personal files were released a good while after his isolation in a solitary cell. He was raised a Christian and took great interest in magic and mind experimenting.
THE WEEK, September 10/September 17, 2021 reports that
Sirhan ... told the parole board he was an "impulsive kid" when he committed "such a horrible deed." Two of RFKs nine surviving children - Douglas and Robert Jr. - spoke in favor of Sirhan's release ... Robert believes a conspiracy theory that Sirhan wasn't the real shooter
I always thought that a hypothetical release of Sirhan would be something of an event on par with Oswald rising from the grave.