Lyle and Erik Menendez were resentenced on Tuesday to life in prison with the possibility of parole, setting the stage for their possible release after more than three decades behind bars for killing their parents in their Beverly Hills mansion.

The decision, by Judge Michael V. Jesic of Los Angeles Superior Court, came after a day of testimony by family members, who said the brothers had turned their lives around inside prison through education and self-help groups. They urged the court to reduce the brothers’ sentences for the 1989 killings.

“This was an absolutely horrific crime,” Judge Jesic said as he delivered his ruling. But as shocking as the crime was, Judge Jesic said, he was also shocked by the number of corrections officials who wrote letters on behalf of the brothers, documented support that clearly swayed his decision.

“I’m not suggesting they should be released,” he said. “That’s not for me to decide.”

But, he continued: “I do believe they have done enough over the last 35 years to get that chance.” The brothers’ futures, he said, would now be in the hands of Gov. Gavin Newsom and state parole-board officials.

While Judge Jesic’s decision was the most important legal step so far in the brothers’ long effort to win release, it is not the final step. In reducing the brothers’ sentences, the judge has allowed them to be immediately eligible for parole.

Now the attention will be on the state’s parole officials. The brothers were already scheduled to appear before the board on June 13 as part of Mr. Newsom’s consideration of clemency, a separate process that has unfolded in parallel to the resentencing effort.

It was unclear if the June hearing would address both the resentencing and clemency request. A spokesperson for Mr. Newsom said his office was reviewing the judge’s decision and determining next steps.

Lawyers for the brothers made only brief statements after the hearing, thanking supporters.

Anamaria Baralt, a cousin of the brothers who testified on Tuesday, faced the dozens of cameras assembled outside the courthouse. “I have been crying all day long. These are tears of joy, for sure,” she said.

Nathan J. Hochman, the Los Angeles district attorney who has opposed resentencing for the brothers, did not provide statements after the ruling. He and his team have argued repeatedly that the brothers failed to demonstrate that they have “full insight” into their crimes. The brothers, they argued, never renounced their claim that they killed their parents because they feared their parents would kill them first, which prosecutors maintained was a lie.

The decision to resentence the brothers is a remarkable turn in a saga that has gripped the nation’s attention for decades. The brothers tried unsuccessfully to appeal their convictions for many years, and they had said that over time, their hopes of being released had diminished. As the years passed, the brothers evolved into cultural icons in their own right, amassing a loyal following as a series of docudramas and documentaries retold their stories for a younger audience.

In 1989, the story of sexual abuse and murder in one of America’s ritziest cities was irresistible to the media and public, and it foreshadowed an even greater obsession with another Los Angeles story — the murder case against O.J. Simpson.

The brothers said they burst into the den of their Beverly Hills mansion on a Sunday evening in 1989 and killed their parents with shotguns because they had endured years of sexual abuse from their father. They said they feared their parents would kill them to keep the abuse secret. At the time, Lyle was 21 and Erik, 18.

Now two middle-aged men, the brothers appeared remotely at the resentencing hearing on Tuesday from their prison near San Diego, sitting stoically in blue jumpsuits while witness after witness testified on their behalf.

After Judge Jesic said that he would resentence the brothers — but before he said what the new sentence would be — the brothers made statements. Through a video feed, they took responsibility for the crimes and apologized to their relatives in the courtroom, who could be heard softly sobbing.

Lyle spoke first, saying that all the choices he made in August 1989 were his own, including “the choice to reload, return to the den and run up to my mother and shoot her in the head.” And he took responsibility, he said, for making a “mockery of the criminal legal system” by lying to the police and trying to solicit others to lie for him on the witness stand at trial.

He said that at the time, he was a young man “scared and filled with rage,” who was too ashamed of the sexual abuse happening in his house to find someone and ask for help.

Erik also took responsibility for the crimes and said he had spent a long time wondering what his parents must have been thinking the night they were murdered, and “the terror they must have felt when their own son fired a gun at them.”

Back then, the case played out as a sort of reckoning of the policies and culture of the 1990s: the tough-on-crime measures that left California’s prisons overcrowded; the societal attitudes about sexual abuse that eyed the brothers’ story with skepticism; the gavel-to-gavel televised trial coverage; and the late-night comics who regularly mocked the brothers as privileged dilettantes.

Their first trial, in 1993, landed during a tumultuous time in Los Angeles. Officers in the beating of Rodney King had been acquitted of assault, catalyzing deadly riots.

After their first trial ended in mistrials — the brothers were tried together with separate juries — they went on trial a second time after Mr. Simpson’s acquittal.

This time, the brothers faced different rules in the courtroom. Cameras were banned, and the judge limited testimony and evidence about sexual abuse. The jury convicted the brothers of murder, and they were sentenced to life in prison without the possibility of parole.

In recent years, the brothers have drawn sympathy from many young people who were not alive at the time of the crimes. Learning about the case online, they have come to believe that the brothers were mistreated by the criminal justice system and the media, and have rallied to their cause on social media.

Laurel Rosenhall contributed reporting.