Rob and Michele Reiner Official Cause of Deaths Revealed

Rob and Michele Reiner died from "multiple sharp force injuries" ... according to the Los Angeles County Medical Examiner.

The ME also notes the manner of death for both Rob and Michele was homicide.

As you know ... Rob and Michele were found dead Sunday afternoon in their Brentwood home.

Rob and Michele's bodies were found by their daughter, Romy, and she told police her brother, Nick, lived with their parents and was "dangerous" and should be considered a suspect.

Nick was arrested on suspicion of murdering Rob and Michele, and he's being held without bail. His arraignment has been pushed back to January, and he's hired Alan Jackson as his defense attorney.

TMZ broke the story ... Rob and Nick got into a heated argument Saturday night at Conan O'Brien's Christmas party, loud enough for others to hear. Rob and Michele left the party after the fight.

Nick was at the party in a hoodie, and we're told the way he was dressed and the way he was behaving made it feel like he was out of place there ... at least that's the way other guests reacted to him.

Rob and Michele's son has been open about his struggles with drugs and addiction and has even been homeless at some points during his life.