Los Angeles, California - Erik Menendez was denied parole Thursday more than three decades after he and his brother Lyle slaughtered their parents in the family's luxury Beverly Hills home.

A California panel ordered the 54-year-old to stay in prison, defying a lengthy campaign waged by family, friends, and celebrities like Kim Kardashian.

"Erik Menendez was denied parole for three years at his initial suitability hearing today," said a brief statement from the California Department of Corrections and Rehabilitation (CDCR).

The result will be a huge blow to a movement that has swelled in recent years, nourished by documentaries and TV dramas, including the smash Netflix hit Monsters: The Lyle and Erik Menendez Story.

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The show and other productions have fixated on the grisly details of the 1989 shotgun murders and the televised jury trial that captivated audiences with accounts of their abusive upbringings and posh lifestyles.

Thursday's hearing came 36 years and a day after his family learned of his parents' deaths, Erik Menendez told the parole board.

"Today is the day all my victims learned my parents were dead," he said during the 10-hour hearing. "So today is the anniversary of their trauma journey."

The parole denial comes the day before Lyle Menendez (57) will appear before a panel to ask them to release him from prison.

"This is a tragic case," parole commissioner Robert Barton said after the decision was issued. "I agree that not only two, but four people, were lost in this family."

More than a dozen relatives testified to say they've forgiven the Menendez brothers, as they came to be known, and to call for their release.

"Two things can be true," Barton said. "They can love and forgive you and you can still be found unsuitable for parole."

The Menendez brothers are among America's most celebrated people in prison, and the stars of one of the first-ever televised murder trials.

Jurors in the 1990s were told how the men killed Jose and Kitty Menendez in what prosecutors said was a cynical attempt to get their hands on a large family fortune.

After setting up alibis and trying to cover their tracks, Erik and Lyle shot Jose Menendez five times with shotguns, including in the kneecaps.

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Kitty Menendez died from a shotgun blast as she tried desperately to crawl away from her killers.

The brothers initially blamed the deaths on a mafia hit, but changed their story several times in the ensuing months.

Erik, then 18, confessed to the murders in a session with his therapist.

The pair ultimately claimed they had acted in self-defense after years of emotional and sexual abuse at the hands of a tyrannical father.

During their decades in prison, changing social mores and greater awareness of sexual abuse helped elevate the men to something approaching cultural icons.

Thursday's hearing, which was closed to the public, was expected to last just two to three hours. Instead, it went on all day.

Erik Menendez appeared by video link from the San Diego prison where he and his brother are being held.

Two or three panel members, whose identity was not released by CDCR, quizzed him on his behavior and attitude towards the murders.

The parole hearing became possible when a judge earlier this year resentenced the men, reducing their original full-life tariff to one of 50 years with the possibility of release.

Los Angeles District Attorney Nathan Hochman, who opposed the resentencing, applauded Thursday's decision.

"Importantly, the (parole) Board did not bow to public spectacle or pressure, a restraint that upholds the dignity and integrity of the justice system."

Lyle's hearing on Friday is independent of his brother's.