Rob Reiner and his wife Michele died of multiple sharp force injuries, the Los Angeles County Medical Examiner’s Office has determined. The manner of death was ruled a homicide.

The couple’s son Nick Reiner has since been charged with two counts of first-degree murder in connection with the deaths of his parents.

Previously, the Los Angeles County District Attorney’s Office said Rob and Michele were stabbed to death in their Los Angeles home during the early morning hours of Sunday, Dec. 14.

Nick was arrested near the University of Southern California several hours after his parents’ bodies were found, authorities said.

Nick made a brief appearance in court Wednesday, shackled and wearing a blue anti-suicide smock. His attorney, Alan Jackson, declined to enter a plea on his client’s behalf, and an arraignment was slated for Jan. 7.

The judge asked Nick, who was seated behind glass, if he was OK with waiving his right to a speedy arraignment.

“Yes, your honor,” he replied.

Rob, who was 78, and Michele, who was 70, wed in 1989 and, in addition to Nick, were parents to son Jake and daughter Romy. Rob was also dad to daughter Tracy, whom he adopted during his decade-long marriage to Penny Marshall in the 1970s. (Tracy’s biological father was Marshall’s first husband, Michael Henry).
The Los Angeles Fire Department previously confirmed to PEOPLE that they received a call to provide medical aid around 3:30 p.m. local time. The LAPD also arrived shortly after and entered the home around 4:20 p.m., and an investigation by the department’s robbery-homicide division is still ongoing.
According to dispatch audio reviewed by PEOPLE, a “unit” was called to Reiner’s address as a code 2; seven minutes later, a request for backup was called and the situation was upgraded to a code 3.

Previously, multiple sources told PEOPLE that Nick and Rob got into an argument at a party at the home of Conan O’Brien the night before the alleged murders, mere hours before Rob and Michele were fatally stabbed.

Rob is a director, producer and actor known for helming many iconic projects, including his directorial debut, This Is Spinal Tap (1984), plus Stand by Me (1986), The Princess Bride (1987), When Harry Met Sally… (1989), Misery (1990) and A Few Good Men (1992).

In 2015, Rob and his son collaborated on the film Being Charlie, which Nick co-wrote and stated was inspired by his own real-life experiences with drug addiction.