US real estate heir Robert Durst was on Friday convicted of killing his best friend to prevent her from being questioned by police about the disappearance of his wife Kathleen, according to US media reports.

This is the first conviction for a man suspected of killing three people in three states over the past 39 years.

The trial came six years after Durst’s apparent confession in the HBO television documentary series The Jinx, in which Durst was caught on a hot microphone in the bathroom saying to himself: “What the hell did I do? … Killed them all, of course.”

Besides The Jinx audio, two other pieces of evidence appeared to damage Durst’s defence. One was the recorded 2017 testimony of Nick Chavin, a mutual friend who said Durst admitted to him in 2014 that he had killed Berman.

“I had to. It was her or me. I had no choice,” Chavin recounted Durst telling him one night after dinner at a New York restaurant.

Prosecutors had said he murdered crime writer Berman in December 2000 to prevent her from being questioned by New York police over the disappearance of his wife Kathleen two decades earlier, according to an AFP report.

He repeatedly denied any involvement in Berman's death, but acknowledged he had written an anonymous letter to police telling them that her body lay in her Beverly Hills home.

Durst, an estranged member of one of New York's wealthiest and most powerful real estate dynasties, was never charged in his wife's case.

He was arrested in March 2015 in a New Orleans hotel room in connection with Berman's murder, hours before the final episode of the HBO documentary "The Jinx: The Life and Deaths of Robert Durst" aired.

The series also delved into the 2001 death of Durst's neighbour in Texas, Morris Black, who was found dismembered.

Durst admitted the dismemberment, but claimed the killing was self-defense. He was acquitted.

"He has never been held accountable for his domestic abuse of (wife) Kathie. He was never held accountable for her death. The last 20 years he's gotten away with murdering Susan," AFP cited Lewin as telling the jury.

"For the last 20 years, he's avoided responsibility for Morris Black. Durst is not jinxed. He's a three-time killer who has managed to escape accountability until this very moment."

Durst will be sentenced on October 18, and faces life in prison.