A cousin of the Menendez brothers is shedding new light on the infamous Beverly Hills murder case.
The brothers were accused of brutally killing their parents, Jose and Kitty, in 1989.
A cousin of Lyle and Erik, who were 18 and 21 at the time of the murders, tells ABC News that the brothers' claims that their father was molesting them was something they had shared with her.
Look back at this notorious case:
The Menendez brothers, jailed for murder of parents
The Menendez brothers, jailed for murder of parents
Erik Menendez (R) and brother Lyle listen to court proceedings during a May 17, 1991 appearance in the case of the shotgun murder of their wealthy parents in August 1989. The California Supreme Court must decide whether to review a lower court decision to allow alleged tape confessions made to a psychiatrist as evidence before a preliminary hearing can take place. REUTERS/Lee Celano
Erik Menendez looks back into the courtroom during a break in the murder trial, August 16 after the prosecution rested its case against him. Erik and his brother Lylem are accused of killing their parents for the inheritance
Defendant Lyle Menendez glances back during a court session August 20, 1993. Menendez and his brother Erik are on trial for the shotgun murders of their parents in 1989. REUTERS/Lee Celano
Lyle Menendez, one of two brothers on trial for the shotgun murder of their wealthy parents, breaks down in tears September 10, 1993 as he recalls incidents of sexual abuse by his father during court testimony. At left are photographs, some showing the genitals of Lyle and brother Erik as children, which the defense claims their father took. Reuters/Lee Celano
Defendant Lyle Menendez wipes his eyes September 10, 1993 as he testifies in a Van Nuys, California courtroom in his defense in the shooting of his parents Lyle and Kitty Menendez. Lyle and brother Erik have admitted to shooting their parents in reaction to years of alleged abuse. REUTERS/Lee Celano
Erik Menendez testifies under cross examination by Deputy District Attorney Lester Kuriyama during a court session October 1, 1993. Kuriyama questioned Menendez's truthfulness in the questioning of the defendant. Menendez and his brother Lyle are on trial for the shotgun murder of their parents. REUTERS/Sam Mircovich
Erik Menendez, one of two brothers accused in the shotgun murder of their wealthy parents, sits silently after a judge refused to pay for his private lawyer to represent him in his retrial March 9, 1994. Menendez pleaded to judge Cecil Mills for public funds to pay for Leslie Abramson, who represented him in his previous trial. That trial resulted in hung juries for both Erik and older brother Lyle. REUTERS/Pool/ Nick Ut
Erik Menendez sits in court July 22 listening to preliminary hearing in his and brother Lyle's murder case, with his attorney Leslie Abrahmson (r). The Menendez brothers both received mistrials in the shotgun killings of their parents Jose and Kitty Menendez in their first trial
Lyle Menendez (R), one of two brothers on trial for the slaying of their wealthy parents, confers with public defender Terri Towery during an October 27, 1994 hearing. Menendez was expected to request the reappointment of his former defense lawyer, Jill Lansing. Reuters/Fred Prouser
Accused murderer Erik Menendez pauses while giving his testimony December 12, 1995, after describing how he and his brother Lyle killed their parents, Jose and Kitty Menendez, in 1989. Erik Menendez testified he was motivated by years of sexual abuse by his father, and the fear that his parents were going to kill him. Lee Celano/Pool/REUTERS
Double murder defendant Erik Menendez mouths the words "I Love You" to his grandmother in the audience as he and brother Lyle are declared guilty of first degree murder with special circumstances in the second trial of the 1989 shotgun slayings of their parents, Jose and Kitty Menendez, March 20. The brothers could face the death penalty for the killings.
Defense attorney Barry Levine (L) pats the back of double murder defendant Erik Menendez (C) while attorney Leslie Abrahmson (R) listens as Erik and Lyle are declared guilty of first degree murder with special circumstances, March 20 in the second trial of the 1989 shotgun slayings of their parents Jose and Kitty Menendez. The brothers could face the death penalty for the killings.
Undated file combo image of brothers Erik (L) and Lyle Menendez who were convicted March 20, 1996 of the first degree murder of their wealthy Beverly Hills parents. The brothers were sentenced to life imprisonment. REUTERS/HO SN
Discover More Like This
BACK TO SLIDE
Diane Vander Molen alleges when she was spending the summer with the boys in 1976, Lyle, then just 8 years old, told her he feared sleeping in his own bed because his father was touching him inappropriately.
"I know that they would never, ever have done what they did unless they felt that they had no choice," Vander Molen told ABC News.
The brothers' molestation claims were central in the sensational 1993 trial. They stand by these claims more than two decades later.
The pair was convicted of shooting and killing their parents in a second trial in 1996, and each are serving two consecutive life sentences.
See more infamous crime cases:
Most famous US crime trials over the past 25 years
Most famous US crime trials over the past 25 years
OJ Simpson: Not guilty in the murder of wife Nicole Brown-Simpson and friend Ron Goldman
O.J. Simpson shows the jury a new pair of Aris extra-large gloves, similar to the gloves found at the Bundy and Rockingham crime scene 21 June during his double murder trial in Los Angeles. Deputy Sheriff Roland Jex (L) and Prosector Christopher Darden (R) look on.
(Photo credit AFP/Getty Images)
Casey Anthony: Not guilty in the murder of daughter Caylee Anthony
Casey Anthony (R) reacts to being found not guilty on murder charges at the Orange County Courthouse on July 5, 2011 in Orlando, Florida. At left is her attorney Jose Baez. Casey Anthony had been accused of murdering her two-year-old daughter Caylee in 2008. (Photo by Red Huber-Pool/Getty Images)
Scott Peterson: Sentenced to death for murder of pregnant wife, Laci Peterson
Scott Peterson listens to the prosecutor during his trial on charges in the murder of his wife, Laci Peterson, on January 4, 2004, in Modesto, California.
(Photo by Bart Ah You/Modesto Bee/MCT via Getty Images)
Martha Stewart: Guilty of conspiracy, obstruction of justice and making false statements to a federal investigator
Martha Stewart leaves US Federal Courthouse after being found guilty 05 March, 2004. The Multi-millionaire lifestyle guru was convicted on charges of conspiracy, obstruction of justice and two counts of making false statements to federal investigators. Each charge carries a maximum sentence of five years in jail. Stewart's stockbroker, Peter Bacanovic, was found guilty on the same counts, but cleared of a separate charge of making false documents. The jury of eight women and four men took a little over two days to reach their decision. Judge Miriam Cederbaum set sentencing for June 17.
(Photo credit TIMOTHY A. CLARY/AFP/Getty Images)
Whitey Bulger: Guilty of racketeering leading to 11 murders
Former mob boss and fugitive James "Whitey" Bulger, who was arrested in Santa Monica, California on June 22, 2011 along with his longtime girlfriend Catherine Greig, is seen in a combination of booking mug photos released to Reuters on August 1, 2011. Bulger, currently on trial in Boston for murder and racketeering, has angrily cursed in open court, his own lawyer has described him as a mobster and one potential witness this week turned up dead on the side of a road. As prosecutors prepare to wrap up their case early next week and hand it over to the defense, the biggest question on observers' minds is whether the 83-year-old defendant will break with convention once more and take to the witness stand.
(REUTERS/U.S. Marshals Service/U.S. Department of Justice/Handout)
Dzhokhar Tsarnaev: Sentenced to death for involvement in the Boston Marathon bombing
A courtroom sketch shows Boston Marathon bombing suspect Dzhokhar Tsarnaev (R) during the jury selection process in his trial at the federal courthouse in Boston, Massachusetts January 15, 2015. Tsarnaev, who appeared in court on Thursday wearing a sport jacket and collared shirt, more formally dressed than in last week's appearances, and had trimmed his hair, is also charged with fatally shooting a university police officer three days after the bombing. He has pleaded not guilty.
(REUTERS/Jane Flavell Collins)
Dylann Roof: Found guilty of killing nine black parishioners at Mother Emanuel church in South Carolina.
Dylann Storm Roof appears by closed-circuit television at his bond hearing in Charleston, South Carolina, U.S. June 19, 2015 in a still image from video.
Timothy McVeigh: Sentenced to death for involvement in the Oklahoma City bombing
Oklahoma City bomber Timothy McVeigh is shown being escorted from the Noble County Courthouse as he is transported to Oklahoma City for arraignment in this April 22, 1995 file photo. One year ago today, on June 11, 2001, McVeigh was executed after being sentenced to death for the bombing of a federal building in Oaklahome City, a crime that took 168 lives and shook a complacent America to the core.
(Photo by Jim Bourg / Reuters)
George Zimmerman: Acquitted of murder in the shooting of Trayvon Martin
George Zimmerman leaves the courtroom a free man after being found not guilty in the 2012 shooting death of Trayvon Martin at the Seminole County Criminal Justice Center in Sanford, Florida, July 13, 2013. Zimmerman was acquitted of all charges on Saturday for the fatal shooting of unarmed black teenager Trayvon Martin in this central Florida town in February of last year.
Dr. Jack Kevorkian: Guilty of second-degree homicide for 'mercy killings'
Dr. Jack Kevorkian is quiet after he was found guilty of second-degree murder and delivery of a controlled substance case in the death of Thomas Youk in a Oakland County Courtroom in Pontiac, March 26. Kevorkian was released on personal bond.
(Reuters Photographer / Reuters)
Michael Jackson: Acquitted on child molestation charges
Michael Jackson leaves the courthouse after being found 'not-guilty' on all charges against him.
(Photo by Bob Riha Jr/WireImage)
Jeffrey Dahmer: Confessed to and was found guilty of 15 murders
Serial killer Jeffrey Dahmer is escorted into a Milwaukee County Circuit Court by a Milwaukee County Sheriffs Deputy for his second appearance in this July, 1991, file photo. Dahmer was found guility of the murders of 16 young men, and sentenced to life in prison in February of 1992.
(Photo via Reuters)
Lyle and Erik Menendez: Found guilty of murdering their parents
Erik Menendez (R) and brother Lyle listen to court proceedings during a May 17, 1991 appearance in the case of the shotgun murder of their wealthy parents in August 1989. The California Supreme Court must decide whether to review a lower court decision to allow alleged tape confessions made to a psychiatrist as evidence before a preliminary hearing can take place.
Jodi Arias: Found guilty in murder of boyfriend Travis Alexander
Jodi Arias is seen in photo from the Arizona Department of Corrections taken April 13, 2015. Arias has been moved to Perryville State Prison west of Phoenix to begin serving her sentence of life with no possibility of parole for shooting and stabbing her ex-boyfriend to death in 2008.
(REUTERS/Arizona Department of Corrections/Handout)
John Allen Muhammad: Sentenced to death for involvement in the Beltway sniper attacks
Sniper suspect John Allen Muhammad (L) listens with his attorney's Peter Greenspun (C) and Jonathan Shapiro during Muhammad's murder trial in courtroom 10 at the Virginia Beach Circuit Court October 22, 2003 in Virginia Beach, Virginia. Muhammad has decided not to represent himself in court and to turn his defense back to his attorneys.
(Photo by Vicki Cronis-Pool/Getty Images)
Rod Blagojevich: Found guilty for extortion and attempting to sell a senate seat
Former Illinois Governor Rod Blagojevich (L) addresses the media while wife Patti Blagojevich holds back tears at the Dirksen Federal Building December 7, 2011 in Chicago, Illinois. Blagojevich was sentenced to 14 years in prison after he was found guilty of 17 public corruption charges.
(Photo by Frank Polich/Getty Images)
Scooter Libby: Found guilty of perjury, obstruction of justice and making false statements to federal investigators
I. Lewis 'Scooter' Libby , former Chief of Staff to Vice President Dick Cheney, arrives at federal court March 2, 2007 in Washington, DC. Jury deliberations continue in the case against Libby. He is accused of lying under oath during an investigation into CIA employee Valerie Plame Wilson's blown cover.
(Photo by Win McNamee/Getty Images)
Rae Carruth: Found guilty of conspiracy to commit murder and shooting into an occupied vehicle in the death of his pregnant girlfriend Cherica Adams
Former NFL player Rae Carruth looks at a Mecklenburg County Sheriff's deputy just after the verdicts were announced in his first degree murder trial in Charlotte, January 19, 2001. Carruth was found not guilty of first degree murder, but the jury returned guilty verdicts on three related charges in the shooting death of his former girlfriend Cherica Adams.
(Photo via Reuters)
Jeffrey Skilling and Kenneth Lay: Found guilty of conspiracy, insider trading, fraud and making false statements in the Enron scandal
Jeffrey Skilling, former president and CEO of Enron Corp., arrives at the Bob Casey Federal Courthouse in Houston, Texas Monday April 17, 2006. Skilling and Kenneth Lay, former chairman of Enron, are on trial for fraud and conspiracy.
(Photo by F. Carter Smith/Bloomberg via Getty Images)
Los Angeles police officer Laurence Powell (L), one of the four defendants in the Rodney King case, waits for the start of his hearing 15 May 1992 in Los Angeles, CA. Judge Stanley Weisberg ruled in favor of a second trial for Powell on brutality charges.
(Photo credit should read POOL/AFP/Getty Images)
Jerry Sandusky: Found guilty pf child sexual abuse.
Former Penn State assistant football coach Jerry Sandusky leaves the Centre County Courthouse in handcuffs after his conviction in his child sex abuse trial in Bellefonte, Pennsylvania, June 22, 2012. A jury found Sandusky guilty on 45 out of 48 counts in his child sex abuse trial on Friday. He was sentenced to between 30 and 60 years in prison.
Ariel Castro: Pled guilty in connection with the abductions and abuse of three women.
Ariel Castro, 53, walks into the courtroom in Cleveland, Ohio July 26, 2013. Accused Cleveland kidnapper Castro agreed to plead guilty and serve life in prison without parole for the abduction and abuse of three women over about a decade. He later committed suicide.