Lyle Menendez breaks his silence 20 years after killing his parents

Lyle, left, and Erik Menendez leave the courtroom in Santa Monica, California. Photo / AP

For the first time in 20 years, Lyle Menendez - who along with his brother killed his parents - has spoken out in a revealing interview with ABC.

"I am the kid that did kill his parents, and no river of tears has changed that and no amount of regret has changed it," Menendez, 48, told ABC News in a recent phone interview as part of a two-hour special called Truth and Lies: The Menendez Brothers.

The special aired yesterday in the US.

"It's shocking to think ... that I could have been involved in taking anyone's life - and my parents' life," Menendez told ABC speaking from Mule Creek State Prison.

"I accept that. You are often defined by a few moments of your life, but that's not who you are in your life, you know.

"Your life is your totality of it ... you can't change it. You just, you're stuck with the decisions you made."

The documentary interviews several people in the 27 years since the brutal crime took place, some of whom revealed they thought it was like something out of a movie or a mafia job.

Menendez and his brother Erik, who at the time were 21 and 18 respectively, shot their sleeping parents Jose and Mary Menendez execution-style in the den of the family's Spanish-style, Beverly Hills mansion on the night of August 20, 1989.

Their father was a successful Cuban-American business executive, their mother a socialite.

Lyle Menendez, left confers with brother Erik during a court appearance, April 2, 1991 in Beverly Hills, California. Photo / AP

They shot Mary several times in her torso and face, leaving her unrecognisable.

Investigators initially believed the killings were a mafia hit, partly due to the fact that both victims had been shot in the kneecaps, but after Lyle confessed to his ex-girlfriend and Erik confessed to a psychologist, the brothers were arrested.

The murder of the wealthy movie executive and his wife had all the elements of a Hollywood film including greed, incest accusations, murder, money and infidelity.

On the night of the couple's murder, police received a distressed call from Lyle Menendez, who told police they had come home from a night at the movies and found their parents shot dead.

Mary had her face blown off, while her husband suffered "explosive decapitation with evisceration of the brain" the autopsy revealed.

"My life is a struggle not to be defined by what happened," Lyle said.

"I'm at peace with my life growing up. I'm at peace with it, because I've just sort of accepted [that] it's okay not to understand."

"It's shocking to think ... that I could have been involved in taking anyone's life - and my parents' life ... it seems unimaginable because it seems so far removed from who I am," he told ABC.

Lyle and Erik Menendez sit inCourt where their attorneys delayed making pleas on behalf of the brothers who are suspected in the murders of their millionaire parents. Photo / AP

After the murders prosecutors said that the brothers killed their parents in an attempt to obtain the family fortune. However, the defence argued that the brothers acted in self-defence after suffering years of sexual abuse from their father.

It took seven years and two trials before the truth was finally revealed and saw the brothers jailed for the crime.

A second trial saw the brothers convicted of two counts of first-degree murder and conspiracy to commit murder and they were sentenced to life behind bars in 1996.

"My own father, he was a person of means and stature, and my mother was sort of a socialite-type person, a country club type person," Lyle said.

"No one's going to intervene in how they raise their family.

"Now you have secrets upon secrets. I was just trapped in the same nightmare of these things that I obviously cannot tell anyone about."

He said he found that his childhood prepared him surprisingly well for the "chaos of prison life."

The two brothers haven't seen each other since a 1995 interview with Barbara Walters and, according to Menendez, they've "almost never talked" about the murders. It's "just too overwhelming".

"I really wondered, separated from me and so on, how would [Erik] do?"

"It's just amazing to me that you can come from such terrible circumstances and then grow up to be someone who is so empathetic, so I'm very proud of him."

Lyle told ABC that Erik now works with terminally ill and physically challenged inmates while he serves his time in Pleasant Valley State Prison in California.

"I'm very proud of him".

And surprisingly both men have found love and married wives while behind bars.

Lyle tied the knot to model Anna Erickson in 1996, before marrying Rebecca Sneed in 2003. His brother has been married to former pen pal Tammi since 1999.

Anna Eriksson sits in a Los Angeles courtroom as she waits for a judge to make a decision on whether she can marry Lyle Menendez. Photo / AP

"I've found I can have a healthy marriage that is complicated and built around conversation and finding creative ways to communicate, sharing, without all the props that are normally there in marriage in terms of going out to dinner and having as much intimate time together and so on," he said.

In California, conjugal visits are strictly off limits to those sentenced to life terms without parole.

"One thing I've learned is that your physical comfort is much less important than your connection with the people around you," he said.

Truth and Lies: The Menendez Brothers - American Sons, American Murderers aired Thursday, January 5, 2017, on US ABC.