Parole panels in California decided this week that Erik and Lyle Menendez should not be released from prison, 36 years after the brothers killed their parents in their Beverly Hills mansion in a sensational crime that later led to a long effort to win their release.

The brothers faced different parole boards, but the outcomes were the same.

On Thursday, a two-person panel denied Erik Menendez parole, citing a series of disciplinary violations in prison that included using drugs, being caught with a cellphone and taking part in a tax fraud scheme.

The next day, a second panel handed Lyle Menendez the same fate, despite the remorse he has expressed and his work for fellow inmates. His disciplinary record in prison appeared better than his younger brother’s, but parole board members cited what they said was a pattern of recent misconduct in prison — including illegally using and selling cellphones. In the hearing he was faulted for persistent “antisocial personality traits,” but praised for showing “potential for change.”

Both panels also touched on the circumstances of the murders themselves. Erik’s panel concluded he was not in “imminent fear” for his life before the murders, rejecting a claim that both brothers have made repeatedly. Lyle’s panel said the killings showed a “remarkable level of callousness and disregard for others.”

The brothers, who were originally sentenced to life without parole for the 1989 killings, were resentenced in May to life with the possibility of parole, setting the stage for this week’s hearings.

The brothers can apply again for parole in three years, though they can petition to come before the board again in as soon as 18 months. They could also seek clemency from Gov. Gavin Newsom of California, or continue their efforts to get a judge to reduce their convictions or grant them a new trial.

On Aug. 20, 1989, the two brothers — then 21 and 18 — walked into the den of the family’s home and fired more than a dozen shotgun rounds at their parents, killing them both.

In recent years, Lyle, now 57, and Erik, now 54, again became objects of fascination thanks to the revelation of new evidence, an army of social media defenders, a recent TV series and a documentary.

Here’s what else to know about the case.

What were the brothers convicted of?

In 1996, the Menendez brothers were found guilty of first-degree murder and sentenced to life in prison without parole for killing their parents, Jose, a music executive, and Mary Louise, a former beauty queen who went by Kitty.

It was their second trial. Two years earlier, a mistrial was declared after two separate juries (one for each brother) deadlocked over a verdict.

The trials proceeded quite differently.

In the first, defense lawyers claimed that the brothers had killed their parents after years of sexual, physical and emotional abuse by their father and that they feared for their lives. Their mother, they said, knew about the abuse but did not stop it.

Interviews with jurors after the mistrial revealed that some of them questioned how serious the abuse had been and to what extent it justified their actions.

In the second trial, which led to their convictions and in which both brothers were tried in front of a single jury, lawyers for the brothers were limited in what evidence could be presented.

The judge, Stanley M. Weisberg, prohibited their lawyers from using the “abuse excuse,” essentially leaving only two options for jurors: an acquittal or a murder conviction. They went with the latter.

New evidence emerged in recent years.

Last year, Roy Rosselló, a former member of the boy band Menudo, revealed in the Peacock documentary “Menendez + Menudo: Boys Betrayed” that Jose Menendez had sexually assaulted him at the Menendez family home in New Jersey when he was 14.

The journalist Robert Rand, who had written extensively about the brothers in his book “The Menendez Murders,” also brought forward a letter that Erik Menendez wrote when he was 17 to his cousin, detailing his father’s sexual abuse.

In a news conference in October, George Gascón, then the Los Angeles County district attorney, said he believed the brothers’ molestation claims and set in motion the resentencing which opened the possibility of parole.

Two Netflix projects brought renewed attention to the case.

The Menendez brothers were the subject of two high-profile releases on Netflix.

The first, “Monsters: The Lyle and Erik Menendez Story,” was an anthology series created by Ryan Murphy which premiered in September.

Weeks later, Netflix released “The Menendez Brothers,” a documentary by Alejandro Hartmann featuring interviews with the two men.

Mr. Gascón previously said that the documentary had “brought a tremendous amount of public attention” and requests for information to his office.

Over the past several years, the Menendez brothers have also been backed by a legion of fans on social media who have examined the case in hindsight and expressed sympathy amid the brothers’ claims of sexual assault.

Their resentencing was opposed by prosecutors.

On May 13, Judge Michael V. Jesic of Los Angeles Superior Court altered the brothers’ sentences to allow the possibility of parole.

The Los Angeles County district attorney, Nathan J. Hochman, a former federal prosecutor who was elected on promises to take a harder line on crime, opposed the resentencing. His office argued in the hearings against granting the Menendez brothers parole, and applauded the decisions of the boards in denying it.

The parole panel heard hours of testimony, including from supportive family members.

The brothers took different approaches to demonstrating their rehabilitation. Erik Menendez has worked more directly to assist fellow prisoners, while Lyle Menendez has been engaged more with prison administrators.

More than a dozen of the brothers’ family members made statements at the hearings as next of kin of their parents, the victims. Victims’ family members typically oppose parole. But this time, all who spoke supported early release.

Robert Barton, the parole commissioner presiding over Erik’s hearing, questioned whether he had been giving his family false information about his prison behavior.

“Contrary to your supporters’ beliefs, you have not been a model prisoner, and frankly we find that a little disturbing,” Mr. Barton said.

Erik Menendez faced hours of questioning from parole board members about the crime and about his rehabilitation efforts.

The hearing for Lyle Menendez lasted more than 11 hours, and was interrupted when the participants learned that an audio recording of his brother’s hearing from the day before had been released to the public.

Some family members then refused to deliver statements, saying that the release of the audio meant there could no longer be a full and fair hearing. The parole board said that it had released the audio legally.

After the second parole board decision, family members released a statement, saying, “While we are of course disappointed by today’s decision as well, we are not discouraged.” They vowed to continue fighting for the brothers’ release.

Reporting was contributed by Kate Christobek, Christine Hauser, Livia Albeck-Ripka Hank Sanders and Jonathan Wolfe