Opening arguments for the Los Angeles murder trial of Robert Durst began this week, four decades after his wife's disappearance set off a string of bizarre crimes and conspiracies involving the real estate heir, whose criminal investigations and alleged confession were the subject of the HBO series The Jinx.

Mr Durst is accused of killing his friend Susan Berman to allegedly stop her from speaking to police about his role in the disappearance of Kathleen Durst, whose body was never recovered after she disappeared in January 1982.

Prosecutors believe he killed his wife near their home outside New York City, and that he shot and killed his friend, who authorities believe may have helped cover up the murder, hours before she was scheduled to speak with police in 2000, reportedly bringing new evidence of the killing to light.

Mr Durst, now 76 and reportedly in poor medical health, has pleaded not guilty to killing Ms Berman and has repeatedly denied his involvement in her death as well as the disappearance of his wife.

As opening arguments in the months-long trial were set to begin on Wednesday, Judge Mark Windham told the courtroom: "Ladies and gentlemen, buckle your seatbelts. We're about to begin."

He was arrested for her murder in 2015, one day before the final episode of The Jinx had aired, in which the last shot appears to incriminate him on a hot mic saying, after presented with potentially crucial evidence: "There it is. You're caught. What the hell did I do? Killed them all, of course."

Prosecutors pressed for his arrest after they had learned that he appeared to admit to several murders in interviews for the documentary.

His trial will reportedly rely on little physical evidence, though a cryptic letter revealed in the TV series could play a significant role.

The series argues that the "cadaver" note – containing only Ms Berman's address and sent to police in Los Angeles to allegedly alert police to her body – could only have been written by Mr Durst.

Defence attorneys had tried to prevent the letter from inclusion in the trial, then reversed their argument, saying that he did in fact write the anonymous note but that it "does not change the fact that Bob Durst did not kill Susan Berman."

In the series' climactic moment, filmmakers confronted Mr Durst with the letter, showing that his handwriting along with his misspelling of Beverly Hills in capital letters was identical in a separate letter to Ms Berman.

A stunned Mr Durst then goes to the bathroom where he utters his "killed them all" comment off-camera. Defence lawyers will point to critical editing that they say wrongly makes his comments appear to be a confession, though authorities said the audio was substantial enough to provide cause for an arrest.

The series also revisits the killing and dismembering of Mr Durst's neighbour Morris Black, whom Mr Durst admitted to killing in self-defence before cutting off parts of his body and throwing them into Galveston Bay in Texas in 2003.