The son of renowned American filmmaker Rob Reiner has been arrested for the murders of his father and mother in their Los Angeles home, with Donald Trump on Monday causing consternation even within his own party by attributing the tragedy to the director's "rabid" anti-Trumpism.

The author of the hit romantic comedy "When Harry Met Sally" and "The Princess Bride," a parody of fairy tales with offbeat humor, was found dead Sunday alongside his wife Michele Singer in their home in Brentwood, an upscale neighborhood of the Californian metropolis.

US media reported that Rob Reiner, 78, and his wife had been stabbed or had their throats slit.

The initial findings of the investigation "reveal that Nick Reiner, 32, the son of Robert and Michele Reiner, is responsible for their deaths," the Los Angeles Police Department said in a statement.

He was arrested shortly after 9:00 PM Sunday evening and placed in pretrial detention on suspicion of murder, she added. He could be formally charged on Tuesday by the local prosecutor's office.

Nick Reiner had a fight with his parents at a party on Saturday night, the Los Angeles Times reports, adding that he has long suffered from addictions.

Trump persists

Before the announcement of the arrest of the victims' son, Donald Trump unleashed a tirade on his Truth social network against Rob Reiner, asserting that his death was the result of his "rabid" anti-Trumpism.

His death "was due to the anger he aroused in others" with his "anti-Trump neurosis," the US president wrote, continuing, in the third person: "He was known for driving people CRAZY with his rabid obsession against President Donald J. Trump."

Criticized for these remarks by members of his own party, Donald Trump nevertheless reiterated his accusations on camera a few hours later at the White House. "He was a disturbed person, in Trump's opinion," he said, still referring to himself in the third person. "I was not a fan of Rob Reiner at all, in any way."

A longtime activist close to the Democrats, the filmmaker was a defender of marriage equality and a vocal critic of the Trump administration.

A friend of the couple, former Democratic Vice President Kamala Harris told X that she was "devastated to learn of their passing" while Barack Obama said that he and his wife Michelle were "heartbroken".

Rob Reiner gave the public "some of our most beloved stories on screen. But behind every story he produced was a deep belief in the goodness of people," the former Democratic president added on X.

"Wonderful friend"

Initially an actor in television series in the 1970s, he began his directing career in 1984 with the film "Spinal Tap" about a fictional rock band. He will be best remembered as the director of numerous cult films such as "When Harry Met Sally" with Billy Crystal and Meg Ryan and "The Princess Bride" with Robin Wright and Mandy Patinkin, as well as films like "Stand by Me" and "Misery".

In 1993, "A Few Good Men" – starring Tom Cruise, Jack Nicholson, and Demi Moore – was nominated for an Oscar. In total, Rob Reiner directed 23 feature films.

Occasionally returning to his acting role, he had recently appeared in four episodes of the series "The Bear".

Actress Kathy Bates, who worked with him on the film "Misery" (1990), said she was "horrified to hear this terrible news".

"I loved Rob. He was brilliant and kind, a man who made films of all genres to push himself as an artist. He also bravely defended his political convictions (...). Michele was a very talented photographer (...). My heart is broken for both of them," the actress said.

Author Stephen King, whose short story "The Body" inspired the filmmaker's classic "Stand By Me" (1986), paid tribute to a "wonderful friend".