The 32-year-old Nick Reiner was arraigned during a brief proceeding that had been twice rescheduled, most recently last month, when his original lawyer abruptly quit without explanation and was replaced by a public defender.
He pleaded not guilty to two counts of first-degree murder in the deadly knife attack on actor-director Rob Reiner, 78, and photographer-producer Michele Reiner, 70, whose bodies were found on December 14 inside their West Los Angeles mansion.
Seated behind a glass partition dressed in brown jail garb, his head shaved and beard closely cropped, Reiner appeared alert but spoke little during the proceeding except to answer "yes" when asked if he agreed to waive his right to a speedy preliminary hearing.
Los Angeles County Superior Court Judge Theresa McGonigle set April 29 as the date for the preliminary hearing, in which prosecutors present evidence intended to show probable cause for proceeding to trial.
Nick Reiner, who has acknowledged a years-long struggle with substance abuse, was ordered to remain in custody, as he has been since his arrest in the hours after his parents were slain.
The killings stirred an outpouring of grief among Hollywood luminaries for Rob Reiner, who first gained fame by co-starring in the 1970s hit television comedy All in the Family and later directed such beloved films as When Harry Met Sally, This is Spinal Tap and The Princess Bride.
Reiner went on to become a prominent Democratic Party activist and donor.
He and his wife, married for nearly 37 years, had planned to attend an evening gathering with former President Barack Obama and Michelle Obama on the day of the murders.
Nick Reiner was widely reported to have quarrelled with his parents while the three were attending a holiday party hosted by comedian Conan O'Brien the night before the couple were slain.
The circumstances and celebrity surrounding the Reiner case have stirred memories of the 1994 stabbing deaths of former football star OJ Simpson's ex-wife Nicole Brown Simpson and her friend Ron Goldman.
OJ Simpson was acquitted of murder charges in a highly sensational case hyped in the media as the "trial of the century," but a civil court jury later found him responsible in a wrongful death lawsuit brought by the victims' families.
If Nick Reiner is convicted as charged, he would face life in prison without the possibility of parole.
Prosecutors have yet to decide whether they would seek the death penalty.
Authorities have disclosed few details about the crime and did not explain what may have precipitated the killings. Autopsies found both victims died of "multiple sharp force injuries."
High-profile defence lawyer Alan Jackson, initially retained to represent Nick Reiner, suddenly withdrew from the case on January 7, forcing the second of two arraignment postponements in three weeks.
Lawyers from the public defender's office were then assigned to take over for Jackson on short notice.
Neither of Nick Reiner's siblings - older brother Jake Reiner, 34, or younger sister Romy, 28, who reportedly was the first to find her father's body - has been present in court for their brother's hearings.
Following his initial court appearance in December, the siblings issued a joint statement expressing the "unimaginable pain" they were experiencing following the "horrific and devastating loss of our parents".
It remained to be seen how Nick Reiner's history of drug addiction, rehab and periodic homelessness might factor into the murder case.
Those struggles inspired the movie Being Charlie, which he co-wrote with his father.
The New York Times reported last week that in 2020, Nick Reiner was placed under a court-approved mental health conservatorship that had allowed for involuntary psychiatric treatment, a legal arrangement that ended in 2021.
