Shocking details from the investigation into the murder of the Reiners. The two were found dead in bed

Rob Reiner and his wife, Michele, were found in bed with their throats slit and may have been killed in their sleep, a source close to the investigation said.

Rob and Michele Reiner were found dead in bed PHOTO Archive

This shocking detail could help establish the timeline of the murders, for which the couple's troubled son Nick, 32, has been arrested, writes the Daily Mail.

The Reiners died sometime between Saturday night — when Nick was seen acting strange and loudly arguing with his parents at Conan O'Brien's Christmas party — and around 3:30 p.m. Sunday, when their daughter Romy called 911 after discovering their bodies in the family's Los Angeles mansion.

“He could have done it shortly after everyone else had gone home, meaning go there and cut their throats in the middle of the night”the source said. “They were in bed when it happened.”

A report on Showbiz 411 suggests that Michele, 70, was still alive when she was found and died in an ambulance en route to hospital after telling first responders that her son was the one who attacked them.

The Los Angeles Police Department has not officially confirmed the details of where exactly the two bodies were found.

TMZ first reported that Reiner, 78, had a “very noisy fight” with his son at O'Brien's holiday party Saturday night, after which the legendary director and his wife left. A party attendee stated that “Nick was freaking everyone out, acting weird and asking people if they were famous.”

Fears for the Reiners' safety only surfaced when a masseuse arrived at their $13.5 million Brentwood, LA mansion at 2pm the next day and no one answered the door. Their daughter Romy, 27, who lives across the road, then investigated the situation and called the emergency services after discovering the horrific scene.

The LA Fire Department says first responders were called to the Reiner home around 3:30 p.m. Sunday and attempted to render aid to the stabbed couple, but were unsuccessful.

Nick, one of the Reiners' three children, lived in the mansion's guest house, a source close to them said. “Nick lived in their guest house, the same one he destroyed several times, but it was like a revolving door his whole adult life”the source said.

“He would do meth and not sleep for days, then throw tantrums, destroy things, punch walls. He was a ticking time bomb. His addiction was getting worse and his parents wanted him out,” the friend added.

Nick himself admitted that a “destroyed” guest house in a drug-induced rage, in a 2018 interview. “We started with the TV, then moved on to the lamp, and gradually everything in the guest house was destroyed”he told host David Manheim, adding that he was “in a state of euphoria” from amphetamines, such as cocaine.

After leaving O'Brien's party, Nick checked into the Pierside Santa Monica Hotel around 4:00 AM on Sunday morning.

A witness told TMZ it appeared “in a strange state”without signs of confrontation. But when the staff went to clean the room later in the morning, the shower was on “full of blood”with blood stains on the bed and sheets used to cover the windows, the source told TMZ.

LAPD detectives investigated and interviewed hotel employees, the website reported.

The director's son was then arrested at 9.15pm on Sunday night, according to his arrest record. He was caught about 15 miles from his home in Brentwood, near a subway station and the University of Southern California campus.