Notorious rich kids Erik and Lyle Menendez have rotted behind bars for more than three decades after killing their parents in cold blood, but now their attorney claims shocking new evidence will set the reviled brothers free!

In a petition demanding a new hearing that could lead to a new trial, lawyer Cliff Gardner says he has irrefutable proof supporting the brothers’ claims they were driven to kill by their predatory father José’s repeated sexual abuse — testimony that was scorned by prosecutors at their 1993 murder trial.

“Erik and Lyle honestly believed they had to take action to save their lives,” says the attorney. “That means they are culpable for manslaughter — not murder. And if that’s the case, they should be released based on the time they’ve already served.”

But the argument could be a hard sell. Erik, now 53, and Lyle, 56, were each convicted of first-degree murder and sentenced to life without parole. The brothers used 12-gauge shotguns to blow away their mom, Kitty, and record exec dad in their Beverly Hills mansion!

José was hit six times. Kitty’s body was mauled by ten brutal blasts. During sensational trials, prosecutors scoffed at the brothers’ claims they were the victims of horrific sexual and physical abuse at their father’s hands while their mom did nothing to help them.

Gardner insists a recently unearthed letter written by Erik and former boy bander Roy Rosselló’s new claim he was sexually abused by José prove the siblings’ story! Gardner says the first crucial piece of evidence is a letter then 18-year-old Erik wrote to his now-deceased cousin Andy Cano detailing the daily sexual abuse by José — and his mother’s knowledge of the twisted doings.

Andy, who died in 2003, supported Lyle and Erik with testimony at their first court case, which ended in a mistrial. He said, “Erik told me his father was massaging his d–k. He told me never to reveal it to anybody.”

Another cousin, Diane Vander Molen, supported those claims. A third cousin, Alan Andersen, also insisted he witnessed the physical abuse. He says he saw José tell the boys, “In the bedroom,” adding, “then he would close the door and then he’d take showers with ’em.” While that was happening, Alan claims Kitty would deliberately keep him away from the room.

But prosecutors managed to keep the cousins’ testimony from being heard at the brothers’ retrial in 1996, when they were convicted.

“The state’s position was Andy Cano was a liar,” says Gardner. “This evidence proves Andy wasn’t making it up.” The second new development is an allegation by Roy, now 53, who claims he was molested by the record boss while he was a member of the boy band Menudo.

After RCA Records honcho José signed the Puerto Rican pop stars to a recording contract, Roy now reveals José gave him a “glass of wine” at his Beverly Hills home, leaving him feeling drugged and with “no control” over his body.

José took him to a room and raped him, the musician claims. “I was in terrible pain for a week,” Roy recalls. “I could barely stand the pain. I couldn’t even move.” Roy adds José abused him twice more in New York before he was delivered into the clutches of the group’s manager, Edgardo Diaz, who’s been accused of similar abuses by the members of the group.

Lyle says those revelations led him to tears. “For me,” he explains, “it was very meaningful to just have things come out that caused people to really realize, OK, at least this part of what it’s about is true.” Gardner believes Roy’s claims are a game-changer.

“The state’s position was the sexual abuse never happened, and José Menendez wasn’t the type of person who would molest a young boy,” he says. “This new evidence takes both those arguments and undercuts them entirely.”

The attorney has filed a petition asking that the Menendez convictions be vacated, and the Los Angeles County District Attorney’s Office says the petition’s claims are being investigated.

“Those boys were abused their whole life,” says Gardner. “This is a manslaughter case, not a murder case. It’s just that simple.”