Transcript for Why Lyle and Erik Menendez Say They Killed Their Parents
Tonight, a rare jail house interview with one of the infamous Menendez brothers who together murdered their parents in their lavish Beverly hills mansion 27 years ago. Were they spoiled kids run amok, or enraged victims of sexual abuse? We're about to hear from witnesses the jury never saw her heard almost three decades later. Are we getting the full story? We warn you, some of the language you're about to hear is extremely graphic. I am the kid that did kill his parents. And no river of tears has changed that. Tonight, Lyle Menendez speaking publicly fra prison in a rare interview, 27 years after he and his brother Eric brutally murdered their parents. It's shocking to think about that happened, that I could have been involved in taking anyone's life. It's still jarring. It seems unimaginable. Seems so far removed from who I am and who I was. Reporter: The glow of innocence founding the Menendez brothers is shattered by charges of murder. To me, it was like a nightmare. Like a movie. Like it couldn't be reality. Reporter: Prosecutors say greed drove the boys to shooting their parents to death last August. One kid killing the parents is a bad seed. Two kids killing the parents is a bad family. I'm just a Normal kid. You're a Normal kid who killed your parents? I know. Reporter: A family saddled with secrets and lies that exploded with this 911 call. What's the problem? What's the problem? Someone killed my dad. Pardon me? Reporter: Tonight the family, friends, and reporters who watched it all unfold -- It's not supposed to happen in Beverly hills. A movie executive and his wife were brutally slain in their million mansion. Reporter: They had been the picture perfect family. They had achieved the American dream. They were living in the mansion in Beverly hills. They were living behind the gate. So on the outside, to most people, this was the perfect, all-American family. People assume that if you have money, you have no problems. And you're certainly not going to do anything like kill your parents. Because you got it made. It turns out that rich people have dysfunctional families just as much as poor people. Reporter: The brothers, who were thought to have it all, at times, acting out, even going as far as robbing houses until they were caught. Joe, when he found out that the children had been arrested, the main message was, how stupid of you to get caught? You're like sheep that follow. You're not leaders. Describe your relationship with your father. Brutal. Painful. Torturous. And yet I admired him because he was so strong, and he was -- he was everything that success was. I think the Menendez brothers were close because they were fighting the common enemy, which was their father. He believed that life is like war and that anything you do to achieve your end is fine. Including, it turns out, killing your parents. Were they shot? Yes! They were shot? Yes! What happened? What happened? Who is the person that was shot? My mom and my dad. Your mom and dad? So you called the police, but at that point you had already decided -- We had decided not -- our feeling was not we'll just explain what happened and it will be okay. We were very stunned and we felt that we would go to jail, obviously, and we -- it was a selfish reason to just not want to have to go through that. As we walked in the front door, it was just eerily quiet. In the back of the foyer was this library family room, which is where the murder occurred. Kitty was wearing white. She was covered in blood. Jose had a shotgun blast to the back of his head, blood everywhere. There was brain matter on the ceiling, on the windows. It was really horrendous. The sons said they discovered the bodies when they arrived home several hours later. We didn't have an alibi. All we did, we said we were at the movies. But they never checked you for gun powder. That day, they didn't. Reporter: For days, theories circulated. Homicide detectives say it could have been a hit. Reporter: But slowly, tips began to trickle in. And ABC news has learned that two 12 gauge shot guns were purchased at this sporting goods store in San Diego on August 18th. Translat Reporter: This time evidence pointing to the Menendez brothers. The glow around them, now shattered by charges of murder. When I saw Eric Menendez walk into the courtroom, my blood went cold, because I had never seen someone who had murdered his parents before. After you entered the den -- I was just firing as I went into the room. I just started firing. In what direction? In front of me. What was in front of you? My parents. There is no issue as to who killed Jose and marylouies Menendez. Why they were killed is what the focus of all of our evidence will be on. Trials are story-telling competitions. Reporter: ABC's Terry Moran, a self-described rookie reporter at the time covered the case extensively for court TV. So whoever tells the better story in the trial that's anchored in the facts as they come out, that's who's going to persuade the jury. The prosecution was completely focused on the idea that Eric and Lyle Menendez were greedy rich kids that had killed their parents because they were in a hurry to inherit their money. Reporter: In the days after the murder, a shopping spree by the brothers. Why did you need to buy a Rolex watch four days after your parents were killed? I didn't need to. Reporter: They made the case that the brothers were afraid of being cut out of their parents' will. But the story took a turn when the defense alleged a deep rooted family secret. He killed his parents because he could no longer endure their abuse and had to stop it. I think there was a near universal sense that this was going to be a sham defense and it was going to be a joke. And then they got on the witness stands. What do you believe was the originating cause of you and your brother ultimately winding up shooting your parents? Me telling Lyle that -- You telling Lyle what? Your honor, can I ask a leading question? My dad -- Wait one second. No, no, he was in the process of answering. So there's no need to ask. Can you answer the question? Yes. Okay, you tell Lyle what? That my dad had been molesting me. You could hear a pin drop in the courtroom. And that's when I thought, oh, darn, I'm in trouble. When Eric Menendez was 10 years old, he told his cousin he had been sexually molested by his father. He told me his father was massaging his . He used that word? Yes, he did. He wanted to know, did this happen to every kid. I do remember very specifically, it was him asking me to make a promise to him never to reveal that to anybody. And between the ages of 6 and 8, did your father have sexual contact with you? Yes. And how did it start? We would have these talks and he would show me, and he would fondle me and ask me to do the same with him. And I would touch him and we would undress. When Lyle appeared, it was a turning point, because now you were hearing a whole different side of the story. And details that no one had ever really heard before. We would be in the bathroom. He would put me on my knee. And he would guide me and my movements. And I would uh, have oral sex with him. The days that Eric and Lyle Menendez testified to their claims of sexual abuse are among the most unforgettable days I've had as a journalist. To this day, my heart catches when I think about that. What else did he do to you? He used objects. What kind of objects? A toothbrush and some sort of shaving utensil, brush. And did he try to anally penetrate you with something else? He did. And what was it? There was a level of detail, it wasn't just explicit. It was accidental. In other words, there are things that people remember from real life that you almost wouldn't kinda make up. Did you tell your brother? No. Did you do something to your brother? Yes. What did you do to your brother? I took him out to the woods. Whenever I felt -- I don't know, I took him out sometimes and I took a toothbrush also and I played with Eric in the same way. And I'm sorry. And he says it with such shame. But what is even more convincing and I was sitting about ten feet from Eric, is, I saw this vein start popping out of his forehead, as he hears his brother apologizing, as their own secret, horrible, sordidness comes out into public, on television. That emotion, that's what a victim, not an actor, that's what a victim looks like. I remember thinking he's either the best actor in the world or this is a true story. It became like a rorschach test. You looked at them and saw cynical, sinister, vicious killers, or you saw victims. Jurors are unable to reach a verdict. Hopelessly deadlocked. Both brothers' trials ended in hung juries. Shortly after America was riveted by the other trial of the century, the second Menendez trial had no cameras in the courtroom. Lyle didn't even take the stand, limiting testimonies about the alleged sexual abuse. The verdict? Lyle and Eric Menendez have been found guilty of murdering their parents. It took a second trial for the two to be convicted of murder in the first degree. What went through your minds when you heard that verdict? That I was going to spend the rest of my life in prison. When we come back, the Menendez brothers find love behind bars. And could there ever be another court case for the convicted killers? Every mother's day, I think about kitty Menendez. Because what they did to their mother was pure unadulterated evil.
This transcript has been automatically generated and may not be 100% accurate.