The Los Angeles County Medical Examiner released the official autopsy results for Rob Reiner and Michele Singer Reiner on Wednesday.
The report states that both Rob and Michele died from multiple sharp force injuries.
Officials officially ruled the deaths as homicides.
Police discovered the couple in their Brentwood home on Sunday afternoon. Romy Reiner found her parents and immediately called for help.
She identified her brother, Nick Reiner, as a potential suspect to the investigators. Law enforcement arrested the 32-year-old Nick later that night.
Prosecutors now charge him with two counts of first-degree murder.
The investigation points to a conflict that began on Saturday night.
Witnesses observed Rob and Nick in a heated argument during a Christmas party at the home of Conan O'Brien. The couple left the event shortly after the confrontation.
Authorities believe Nick killed his parents in the early hours of Sunday morning.
Nick appeared in court on Wednesday wearing a suicide vest and shackles. His lawyer, Alan Jackson, asked the judge to delay the proceedings until January.
Nick has struggled with addiction and homelessness for years.
He and Rob previously collaborated on a film about these struggles titled Being Charlie. Rob Reiner was 78 and Michele Singer Reiner was 70.