Rob Reiner and Michele Reiner attend a wedding ceremony and celebration in June 2014 at The Beverly Hilton. Lester Cohen/Getty Images for Hilton Hotels & Resorts

Filmmaker Rob Reiner and his wife Michele died of "multiple sharp force injuries," the Los Angeles County Medical Examiner's Office reported Wednesday. This comes after authorities had previously confirmed that the couple were fatally stabbed.

Rob Reiner, 78, and Michele Singer Reiner, 70, were found dead Sunday afternoon at their home in the upscale L.A. neighborhood of Brentwood, police said.

Their son, 32-year-old Nick Reiner, has been charged with two counts of first-degree murder with special circumstances in their slayings, Los Angeles County District Attorney Nathan Hochman announced Tuesday. The charges include "a special allegation that he personally used a dangerous and deadly weapon, a knife," according to the DA's office.

Investigators believe Nick Reiner fatally stabbed his parents early Sunday morning before fleeing, prosecutors said.

The bodies of Rob and Michele Reiner were found at about 3:40 p.m. Sunday, police said, and Nick was found and arrested in the Exposition Park neighborhood of South L.A. at approximately 9:15 p.m. Sunday. Authorities have yet to provide a possible motive in the killings or what led them to arrest Nick Reiner.

Two sources who attended a party Saturday night at Conan O'Brien's home, where Rob and Nick Reiner were also present, told CBS News on Monday that a brief but loud argument between the two took place.

Nick Reiner's movements following the murders are under investigation. CBS News learned Wednesday that he checked into a hotel in Santa Monica early Sunday morning, which is about four miles away from his parents' Brentwood home. Security video obtained Tuesday also showed him inside a gas station convenience store just before his arrest.

His first court hearing was Wednesday, and his arraignment is scheduled for Jan. 7.

Hochman said the charges carry a maximum sentence of life in prison without parole or the death penalty, but that his office hasn't decided which to pursue.

Rob and Michele Reiner married in 1989 and had three children together. Their two other children, Jake and Romy Reiner, released a statement Wednesday calling the loss of their parents "horrific and devastating."

"They weren't just our parents; they were our best friends," the statement reads.

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