Menendez Brothers Say New 'Menudo' Evidence Backs Up Sex Abuse Allegations Against Dad

The Menendez Brothers want to have their day in court ... again ... they say they have new evidence backing up their defense that their father was sexually abusing them, but there's a new wrinkle involving a member of the '80's boy band "Menudo."

According to new legal docs filed by attorney Mark Geragos, and obtained by TMZ, Erik and Lyle Menendez cited recent allegations by former Menudo star Roy Rossello that he was sexually abused when he was 13 or 14 by Jose Menendez.

Rosello made the accusations against Jose -- a then-RCA record exec -- in a new three part Peacock docuseries, "Menendez + Menudo: Boys Betrayed." In the series, two journalists dove into claims that the band's founder, Edgardo Diaz, brought Rosello to Jose's home in New Jersey to broker a deal between "Menudo" and RCA. But things took a dark turn when Jose allegedly drugged Rossello and then raped the teen.

Per the court docs, Erik and Lyle argued that Rossello's allegations of abuse by their dad only served to strengthen their original contention that they fatally shot Jose and their mom, Kitty, out of self-defense.

The petition also mentioned a letter Erik sent to their cousin, Andy Cano, months before the shootings ... where Erik accused Jose of sexual abuse.

In the letter, which the brothers claimed wasn't shown to the jury at trial, Erik says he wished he could tell his mom about the alleged abuse but says he can't risk it because he feared she would tell Jose. Erik also told Andy his father was continuing to molest him.

The Menendez Brothers say the letter was sent around 8 months before they murdered their parents, and they argued it supported their defense theory that Jose was sexually abusing them and warned them to not speak out about being molested, to the point where they became frightened of their father.

They say jurors never heard from Roy either, and they claimed if the jury knew about Roy's allegations and the letter, things might have turned out differently and they might have bought the defense's theory that the brothers were guilty of manslaughter, instead of murder.

Erik and Lyle filed a petition for a writ of habeas corpus in an effort to determine whether the new evidence was enough for the court to grant them a new trial or other relief.

Attorney Alan Jackson talked to us in April about the possibility of the Menendez brothers getting a new trial ... and he didn't seem to think it was likely, and told us exactly why.