Rob Reiner and his wife Michele were found in bed with their throats cut and may have been asleep when they were murdered, a source close to the investigation claimed to the Daily Mail.

The gruesome detail could help establish a timeline of the killings, for which the couple’s 32-year-old troubled son Nick has been arrested.

The Reiners died some time between Saturday evening – when Nick was seen acting erratically and arguing loudly with his parents at Conan O’Brien’s Christmas party – and around 3.30pm on Sunday, when their daughter Romy called 911 after having discovered their bodies at the family’s Los Angeles mansion.

‘He could have done it not long after they all went home, meaning he went there and slit their throats in the middle of the night,’ the source claimed. ‘They were in bed when that happened.’

One report on Showbiz 411 suggests Michele, 70, was still alive when she was found and died in the ambulance on the way to the hospital after she had told first responders her son was the one who attacked them.

The Los Angeles Police Department has not officially confirmed any details of where in the house the Reiners’ bodies were found.

But the claim that his parents were found dead in their bed could suggest a small mercy in the tragic incident: that they may have been killed in their sleep.

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Rob Reiner, 78, and his wife Michele were allegedly found in their beds with their throats slit after their daughter Romy called 911, sources exclusively told the Daily Mail

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The couple’s troubled son Nick Reiner, 32, has been arrested for their murders which allegedly occurred after a turbulent night of fighting at Conan O’Brien’s Christmas party on Saturday

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The front of late-night host Conan O’Brien’s mansion, the scene where Nick was reportedly acting erratically and locked in an intense argument with Rob and Michele during the party

TMZ first reported that Reiner, 78, had a ‘very loud argument’ with his son at O’Brien’s holiday bash on Saturday night, after which the legendary movie director and his wife left.

One partygoer told People magazine that ‘Nick was freaking everyone out, acting crazy, kept asking people if they were famous’.

Fears for the Reiners’ safety were only raised when a masseuse arrived at their $13.5 million mansion in the Brentwood district of LA at 2pm the next day and no one answered the door, the Daily Mail previously revealed.

Their 27-year-old daughter, Romy, who lives across the street, then reportedly investigated and called emergency services when she discovered the horrific scene.

The LA Fire Department says first responders were called to the Reiner home around 3.30pm on Sunday and tried to render aid to the stabbed couple, to no avail.

Nick, one of the Reiners’ three children, had been living in the mansion’s guest house, a source close to him told the Daily Mail.

‘Nick had been living in their guesthouse, the same one he destroyed more than once, but it had been like a revolving door all his adult life,’ the source said.

‘He would do meth and not sleep for days and then have outbursts, breaking things, punching walls.

‘He was a ticking time bomb. His drug use was getting worse and his parents wanted him out,’ claimed the friend.

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Nick had been living in his parents’ guesthouse for the past five years as he battled drug addiction, sources told the Daily Mail. Though he has spoken of living on the streets, he posted this image on social media in 2015 with the caveat: ‘This is a set’

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Nick’s sister Romy, who lived across the street from their parents, was the one who went to check on the house after no one had heard from Rob or Michele

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Reiner and his wife Michele were found dead at their $13.5 million six-bed Brentwood home

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The director’s son was arrested at 9.15pm on Sunday night, booking records show. Bail on the murder charges was initially set at $4 million but this was later revoked

Nick himself admitted to ‘wrecking’ the guest house in a drug-fueled rage, in a 2018 interview on addiction podcast Dopey.

‘I started with the TV and then I went over to the lamp and then [progressively], just everything in the guest house got wrecked,’ he told host David Manheim, adding that he was ‘spun out on uppers’ like cocaine.

After leaving the O’Brien party, Nick allegedly checked into The Pierside Santa Monica hotel around 4am on Sunday.

A witness told TMZ he appeared ‘tweaked out’, though with no signs of a confrontation.

But when staff went to clean his room later that morning, the shower was ‘full of blood’, with blood stains on the bed and the bed sheets covering the windows, the source told TMZ.

LAPD homicide detectives have investigated and interviewed hotel workers, the site reported.

The director’s son was then arrested at 9.15pm on Sunday night, according to his booking record.

He was picked up about 15 miles away from the Brentwood home, near a Metro station and the University of Southern California campus, the LA Times reported.

He is currently in the Twin Towers Correctional Facility in downtown LA and had been expected to appear in court on Tuesday. However, his attorney Alan Jackson said he had not been medically cleared to appear.

It is customary for a defendant to be arraigned at their first court appearance, where they are advised of the charges against them, they are given the opportunity to enter a plea and bail can be discussed.