Rob Reiner, 78, and Michele Singer Reiner, 70, were found dead in their home by their daughter on 14 December.
The couple died from “multiple sharp force injuries”, according to the LA County medical examiner.
Nick Reiner was arrested in Los Angeles the same day. US outlets reported that he and his father had attended a party the previous evening, and engaged in an argument of some kind. Reports vary as to the severity of the alleged row.
He faces two counts of first-degree murder, with a special circumstance alleging multiple murders.
Rob Reiner directed films including This Is Spinal Tap, the Princess Bride, When Harry Met Sally and Stand By Me.
Michele Singer Reiner was an actress, photographer and producer, and the founder of Reiner Light, a photography agency and production company.