Nick Reiner, who has been arrested in connection to the murders of Rob Reiner and Michele Singer Reiner, “freaked out” and had a huge blow-up with his parents at Conan O’Brien’s Christmas party a day before the murders, a source told the New York Post.

Rob and Michele’s bodies were found inside their Brentwood home on Sunday, December 14. Los Angeles police said in a statement that Nick was “responsible” for the deaths, according to CNN.

What happened at Conan O’Brien’s Christmas party?

Nick had a “very loud argument” with Rob and Michele at the party, possibly fueled by him going back on drugs and refusing treatment, the source added. Nick has reportedly been in and out of rehab for his drug addiction.

“They had had an argument at Conan’s holiday party, and Rob had been telling people that they’re scared for Nick and scared that his mental state was deteriorating,’’a lifelong family friend who lives near the Reiner home told the outlet.

Read More | Nick Reiner: 5 things to know about Rob Reiner’s son who was arrested after parents’ deaths

“Nick was supposedly off drugs,” but then rumors surfaced that he was “not so much off them,’’ the neighbor added.

Nick was, at his lowest points, “badly addicted to a combo of opiates and heroin,” the family friend claimed.

Sources told People that Nick and Rob got into a “big fight” at the party. “Nick was freaking everyone out, acting crazy, kept asking people if they were famous,” one of the sources said.

Two people familiar with the incident at O’Brien’s party said, according to NBC News, that Nick was disruptive at the event. Another person said his parents were upset and embarrassed about his behavior at the party.

Read More | Where is Nick Reiner being held? Rob Reiner’s son placed on suicide watch after arrest

One person said that Nick made other guests uncomfortable with his behavior at the holiday party. Nick, Rob and Michele attended O’Brien’s gathering together, where Nick had at least one interaction that left partygoers concerned, a person familiar with the situation said.

Nick allegedly interrupted a conversation involving comedian Bill Hader. When Hader told Nick the conversation was private, Nick seemed to stand still and stare before “storming off,” a source said.

Nick Reiner placed under suicide watch

Nick’s sister Romy is beloved to have found the bodies of their parents on Sunday, December 14. She told investigators that Nick was “dangerous” and “should be a suspect.” Nick was arrested hours after his parents’ murders.

Nick, 32, is now being held in administrative segregation and on suicide watch. He is behind bars at Twin Towers Correctional Facility in Los Angeles, law enforcement sources told TMZ. He has been arrested on murder charges and is being held without bail.