Attendees of Conan O’Brien’s holiday party the night before Hollywood director Rob Reiner and his wife, Michele Reiner, were murdered could be called as witnesses in the next phase of their son Nick Reiner’s murder case, Us Weekly can reveal.

“A plea of not guilty at arraignment on a serious like this case is very much a routine part of the process. Each side has a significant amount of work before the case moves forward, including reviewing police reports, witness interviews, medical records, and doctors’ reports,” former Los Angeles County deputy district attorney, now criminal defense attorney, RJ Dreiling of Dreiling Law APC exclusively told Us. (Dreiling is not in any way associated with the case.)

Nick, 32, entered a not guilty plea to two counts of first-degree murder in a Los Angeles courthouse on Monday, February 23, after being accused of fatally stabbing his parents in December 2025.

Before Rob, 78, and his wife, 70, were killed, the pair attended the comedian’s holiday party. It was later reported that the This Is Spinal Tap director got into a verbal argument with his son during the festivities. Nick also allegedly had an uncomfortable encounter with Bill Hader that same evening.

Now, those in attendance could potentially be called to describe their version of events under oath, according to Dreiling. (Nick’s preliminary hearing is set for April 29.)

“At that hearing, prosecutors must convince a judge there’s enough evidence to go to trial and they do this through calling witnesses. I would expect that we may hear directly or indirectly from witnesses at Conan O’Brien’s Christmas party to talk about what they saw happen between Nick and his parents,” Dreiling explained. “The prosecutor will use this as a motive. Right now, that hearing is on pause while each side continues to work on their case.”

Rob and Michele were stabbed to death in their home in the Brentwood neighborhood of Los Angeles on December 14, 2025. Nick was later arrested and is currently being held without bail after being formally charged with two counts of first-degree murder.

Nick’s alleged behavior at O’Brien’s holiday party has been widely reported – TMZ claimed he got into a “very loud argument” with his father in the presence of several potential witnesses.

Related: What Did Nick Reiner Say to Bill Hader? Inside Their Christmas Party Exchange

Nick Reiner allegedly had a strange encounter with former Saturday Night Live star Bill Hader hours before he allegedly murdered his parents, Rob Reiner and Michele Singer Reiner. Multiple media outlets reported that both men attended Conan O’Brien’s Christmas party on December 13, 2025. According to Rolling Stone, the Reiners asked if they could bring […]

A source confirmed to Us that Nick was allegedly acting “creepily” toward party guests, at one point “asking if they were famous.”

The alleged argument with Rob could derail Nick’s defense, Neama Rahmani, president of Los Angeles-based West Coast Trial Lawyers, exclusively told Us. (Rahmani is not in any way associated with the case.)

“The fact that Nick got into an argument with the victims a day before the murders at Conan O’Brien’s Christmas party is fatal to any real defense in the case,” he shared on Monday.

As for O’Brien, 62, he recently broke his silence on Rob and Michele’s death.

Related: Nick Reiner Has Shaved Head, Sits Behind Glass in Eerie Courtroom Photos

Nick Reiner was photographed during his most recent court appearance for the murders of his parents, Rob Reiner and Michele Singer Reiner. Nick, 32, arrived in the Los Angeles courtroom on Monday, February 23, wearing a brown jumpsuit. He sported a shaved head with facial hair. While in the courtroom, Nick sat behind glass. During […]

“I knew Rob and Michele, and then increasingly got closer and closer to them, and I was seeing them a lot,” he told The New Yorker in an interview published on Friday, February 20. “My wife and I were seeing them a lot, and they were so — they were just such lovely people. And to have that experience of saying goodnight to somebody and having them leave and then find out the next day that they’re gone.”

He continued, “I think I was in shock for quite a while afterward. I mean, there’s no other word for it. It’s just very — it’s so awful. It’s just so awful. And I think about how Rob felt about things that are happening in the country, how involved he was, how much he put himself out there — and to have that voice go quiet in an instant is still hard for me to comprehend.”

If convicted, Nick could face the death penalty or life in prison without parole.