Nick Reiner, 32, is charged with killing the 78-year-old actor and director Rob Reiner and his wife, Michele Singer Reiner, District Attorney Nathan Hochman announced at a news conference with LA Police Chief Jim McDonnell.
"Their loss is beyond tragic and we will commit ourselves to bringing their murderer to justice," Hochman said on Tuesday.
The charges carry a maximum penalty of life in prison without the possibility of parole, or capital punishment, but prosecutors have yet to decide whether to seek the death penalty.
Hochman said prosecutors "will take the thoughts and desires of the family into consideration" in making such decisions.
The killings ranked among the most shocking celebrity murders in Los Angeles history, eliciting comparisons by some to the stabbing deaths of OJ Simpson's ex-wife Nicole Brown Simpson and a friend, Ron Goldman in 1994.
Along with the two counts of first degree murder, prosecutors added special circumstances of multiple murders and a special allegation that the defendant used a dangerous weapon, a knife.
The additions could mean a greater sentence.
The announcement came two days after the couple was found dead from apparent stab wounds in their home in the upscale Brentwood neighbourhood on the west side of Los Angeles.
Nick Reiner did not resist when he was arrested hours later in the Exposition Park area near the University of Southern California, about 22km from the crime scene, police said.
Nick Reiner had been expected to make an initial court appearance earlier on Tuesday, but his lawyer Alan Jackson said he was not brought from the jail to the courthouse for medical reasons and the appearance would not come before Wednesday.
Jackson is a high-profile lawyer who represented Harvey Weinstein at his Los Angeles trial.
Various news media outlets have reported that Nick Reiner had been seen quarreling with his parents on Saturday night at a holiday party hosted by comedian Conan O'Brien.
Nick Reiner, the younger of the Reiners' two sons and their middle child, has publicly acknowledged a years-long struggle with substance abuse. He has remained held without bail at a Los Angeles County lockup since he was booked on suspicion of murder on Sunday night.
Rob Reiner was the Emmy-winning star of the sitcom All in the Family who went on to direct films including When Harry Met Sally and The Princess Bride.
He was an outspoken liberal activist for decades. Michele Singer Reiner was a photographer, movie producer and advocate for LGBTQ+ rights. They had been married for 36 years.
The killings were especially shocking given the warm comic legacy of the family. Rob Reiner was the son of comedy legend Carl Reiner, who died in 2020 at age 98.
Three months ago, Nick Reiner was photographed with his parents and siblings at the premiere of his father's film Spinal Tap 2: The End Continues.
He had cycled in and out of treatment facilities with bouts of homelessness in between through his teen years. Rob and Nick Reiner explored - and seemed to improve - their relationship through the making of the 2016 film, Being Charlie.
Nick Reiner co-wrote and Rob Reiner directed the film about the struggles of an addicted son and a famous father. It was not autobiographical but included several elements of their lives.
President Donald Trump on Monday blamed Rob Reiner's outspoken opposition to the president for the actor-director's killing, delivering the unsubstantiated claim in a social media post that seemed intent on decrying his opponents even in the face of a tragedy.
with Reuters
