US real estate heir Robert Durst was on Thursday sentenced to life imprisonment for the cold blooded murder of his best friend.

Durst, a multi-millionaire who featured in an explosive HBO documentary entitled "The Jinx," has always denied charges that he shot his friend, Susan Berman, in the back of the head in 2000 at her Beverly Hills home as she had been called by the police for questioning about the disappearance of his wife two decades earlier.

Durst was scared about the possibility of Berman giving evidence against him under police pressure. She was the daughter of a Las Vegas mobster and had acted as a spokeswoman for Durst after he became a suspect in his wife's disappearance.

Last month, a jury in Los Angeles found the 78-year-old guilty of the execution-style slaying of Berman.

"This crime was a witness killing," Judge Mark Windham said before reading out the life sentence. "That circumstance… tremendously aggravated this awful, disturbing crime," according to an AFP report.

Windham rejected the defense's request for a new trial, saying, "There is sufficient, in fact, overwhelming evidence of guilt."

The court also heard from Sareb Kaufman, a son of Berman who said he has wondered what his life would have been like had Durst not killed his mother.

"Every plan was completely swept away," a crying Kaufman said. "You also murdered me, the person I was."

Durst sat motionless in a wheelchair during Thursday's court session.

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.”