At his trial for the murder of Robert F. Kennedy, Sirhan Sirhan testified that when he gunned down the charismatic Democratic presidential candidate in 1968, he did so “with 20 years of malice aforethought.”

An Arab Christian from Jerusalem, Sirhan hated Kennedy for his support of Israel. Though “20 years of malice” was hyperbole — Sirhan, who was 24 when he opened fire in the crowded kitchen of the Ambassador Hotel in Los Angeles, had presumably not been plotting his crime since early childhood — there was evidence aplenty that his assassination was meticulously planned. He had visited the hotel to study its layout and gone to a gun range the day before the killing to practice shooting. In his personal journal he described his “determination to eliminate R.F.K.” as “an unshakable obsession,” and wrote: “Robert F. Kennedy must be assassinated before June 5, 1968.”

Sirhan’s guilt was never in question: He murdered his victim before scores of eyewitnesses, including news reporters and photographers. After finding him guilty of first-degree murder, a California jury unanimously returned a verdict of death, rejecting the defense attorney’s argument that a life sentence would suffice. Sirhan escaped the punishment he deserved only because the California Supreme Court ruled in 1972 that the death penalty violated the California Constitution. All inmates then on death row had their sentences commuted to life imprisonment. California at the time had no life-without-parole option, so the state’s most abhorrent killers (Charles Manson was another) ended up with a sentence no judge and jury had ever approved: a life term with the possibility of parole.

That was a miscarriage of justice. But it was nothing compared with the grotesque decision by two members of the California parole board, who recommended Friday that Sirhan, now 77, be released from prison on the grounds that he no longer poses a threat to society.

To my mind, no one convicted of first-degree murder and sentenced to life imprisonment — assuming their guilt is undisputed — should ever be paroled. A life sentence should preclude the possibility of ever again walking free. Regrettably, that isn’t the law in California, and Sirhan has applied for parole 16 times. Every previous application was opposed by prosecutors, but the policy of the current Los Angeles district attorney, George Gascón, is to support parole in nearly all cases, and under no circumstances to actively oppose it. His view is that inmates who are no longer considered dangerous do not belong behind bars, notwithstanding the magnitude of their crimes.

But present dangerousness is not the only reason criminals are imprisoned, and should not be the only criterion for release — especially not when it comes to murderers whose crimes were so appalling that the judge and jury concluded (and the appellate courts agreed) that they should spend the rest of their lives in prison. The aging Sirhan may be unlikely to kill again. But time has not mitigated the evil he committed. It is meaningless to speak of Sirhan’s “rehabilitation” and “remorse,” not least because for years he has denied having any memory of the murder. (Even more absurdly, he has sometimes claimed that RFK was his “hero” and his “champion.”)

For lesser crimes, it may be appropriate to parole prisoners who have genuinely repented and worked to become better human beings. But for a crime like Sirhan’s, no rehabilitation can justify a return to society. To die in prison is admittedly a terrible fate. Yet a civilized system of justice demands the most terrible punishment for the most terrible crimes.

What made Sirhan’s crime so terrible was not primarily that it was a political assassination, that his victim was a presidential candidate, that he altered the course of US history, or that he murdered a member of a prominent family. It was that he destroyed the life of an innocent person willfully, violently, and mercilessly. There is no escaping the political nature of what happened at the Ambassador Hotel on June 5, 1968. But if Sirhan had carefully plotted and deliberately carried out the murder of a busboy in that hotel kitchen, he would deserve the same punishment.

Like James Earl Ray, Byron De La Beckwith, and Whitey Bulger — murderers sentenced to life imprisonment who took their last breath behind bars — Sirhan forfeited his right to ever again live in freedom. Maxwell Kennedy, one of Robert Kennedy’s sons, wrote the other day that “the mere thought” of his father’s killer being released makes him sick. Such a travesty of justice should sicken us all.

(Jeff Jacoby is a columnist for The Boston Globe).