Rob and Michele Reiner's Cause of Death Revealed After Their Lifeless Bodies Were Discovered Inside Mansion by Horrified Daughter

Rob and Michele Reiner's cause of death has been determined to have come from "multiple sharp force injuries," RadarOnline.com can reveal.

The Los Angeles County Medical Examiner announced what killed the legendary actor-director and his wife, classifying their deaths as "homicides" with their date of death listed as Sunday, December 14.

The couple's son, Nick, 32, has been officially charged with two counts of first-degree murder with special circumstances for allegedly slitting his parents' throats after the trio arrived home from a Christmas party on December 13. He was arrested the following day, after Nick's sister, Romy, discovered her parents' lifeless bodies inside their longtime Brentwood, California, mansion.

Nick, who has a long history of drug abuse and mental illness, made his first court appearance on Wednesday, December 17. His arraignment was postponed until January 7, so his legal team can get up to speed on his case.

If convicted, he faces life in prison without parole, and Los Angeles County District Attorney Nathan Hochman revealed that the death penalty is still on the table.

High-profile criminal defense attorney Alan Jackson has been hired as Nick's counsel.

The medical examiner's determination the When Harry Met Sally director and his wife of 36 years died as a result of "multiple sharp force injuries" tracks with other reported details about the gruesome stabbings.

Nick used his own credit card to check into a nearby Santa Monica hotel room around 4 a.m. on Sunday, December 14, where an eyewitness claimed he appeared "tweaked out."

Later that morning, housekeeping arrived at the room he had since vacated to find the shower "full of blood" with more blood on the bed. It appeared Nick had also taken sheets from the bed to cover the room's windows and block out the light.

He was picked up that evening after 9 p.m., nearly 20 miles away in the Exposition Park area of Los Angeles, where LAPD officers and US Marshals took him into custody without incident.

Events leading up to Rob and Michele's brutal slayings suggest a fight between the father and son at Conan O'Brien's A-list Christmas party may have sent tempers flaring.

Nick was living in the couple's guest house, and they were reluctant to leave him at home alone out of concern for his increasingly erratic well-being. They reportedly asked O'Brien if their son could accompany them to the party.

Once there, "Nick was freaking everyone out, acting crazy, kept asking people if they were famous," one insider revealed.

At one point, Nick reportedly approached comedian-actor Bill Hader, with an eyewitness claiming he "interrupted" the Barry star's conversation with a fellow guest. After being politely told it was a private discussion, "Nick just stood there and stared before storming off," the witness said, alarming other partygoers.

After the incident with Hader, other eyewitnesses claimed Rob and his son "had it out" over "Nick’s asocial and unsettling behavior," causing other partygoers to notice the heated discussion.

Soon after, a "mortified" Rob and Michele reportedly apologized to O'Brien for the scene at his party and left to head home. However, it remains unclear if Nick accompanied his parents back to their estate.

However, a source close to the Reiner family told The NY Times, "Rob and Nick Reiner did not have a heated argument" and claimed the "episode was being overblown."

They added: "The intensity of any conversation that might have taken place between father and son may have been misinterpreted."