Two decades after Lyle and Eric Menendez murdered their parents in the California home, the eldest brother opened up about the infamous 911 call, in which he sobbed uncontrollably as he told an operator his parents were killed.

In an interview with NBC News’ Keith Morrison, which appears on Dateline on Friday night, Lyle explained that him and his brother were in such a “state of trauma” that it didn’t quite register yet what they had done.

“I think I was just absolutely broken down with stress. Both of us were just in such a state of trauma and I just — it didn’t pour through on that call. It made it very easy to make that call, really.”

On August 20, 1989, 21-year-Lyle and 18-year-old Eric killed their parents, José and Kitty, in the living room of their Beverly Hills home at 722 North Elm Drive. The pair was found shot to death by a Mossberg 12-gauge shotgun, apparently taken by surprise as they watched television. Neighbors reported hearing loud banging that night at around 10 p.m. At around 11:47 p.m., Lyle called 911 and screamed, “Somebody killed my parents!”

The 911 call become one of the most notorious calls made to 911 in history.

The brothers claimed they shot their parents in self-defense after enduring years of mental, physical, and sexual abuse. Prosecutors alleged the boys wanted to take over their parents’ $14 million estate. Ultimately, both brothers were sentenced to life without the possibility of parole.

For the full interview, watch Dateline‘s Unthinkable: The Menendez Murders on Friday at 9 p.m. ET on NBC.

[Feature Photo: Lyle Menendez/AP/Nick Ut]