Mystery witness to testify against Robert Durst of 'The Jinx'
Real estate heir Robert Durst appears in a criminal courtroom for his trial on charges of trespassing on property owned by his estranged family, in New York on Dec. 10, 2014. Photo by Mike Segar for Reuters.

Robert Durst, the real estate scion tied to several slayings explored in HBO's series "The Jinx," returned to a Los Angeles courtroom on Wednesday to face a prosecution witness whose identity was being kept secret until taking the stand.

Durst, 73, is charged with first-degree murder in the fatal shooting of a writer and longtime confidante of his, Susan Berman, in December 2000, and prosecutors say the secret witness fears his or her life may be put in danger by testifying.

Berman was found slain execution-style in her Los Angeles home not long after police in New York had reopened an investigation into the disappearance and presumed killing of Durst's spouse, Kathleen, two decades earlier.

Prosecutors in Los Angeles say they suspect Durst killed Berman, 55, because of what she knew about his wife's unsolved demise in 1982.

The judge has given approval for Wednesday's witness to testify well in advance of the actual trial, with questioning and cross-examination by both sides videotaped and preserved in the event anything should prevent the person from appearing in court later.

An 85-year-old retired dean of the New York City medical school attended by Durst's wife before she vanished was permitted to testify under similar conditions on Tuesday due to his advanced age.

Durst has pleaded not guilty in the murder case and said he had nothing to do with the fate of either woman. He was questioned in the probe of his wife's disappearance but has not been charged, and her body has never been found.

His ties to both cases, and his 2003 acquittal in the killing and dismemberment of a Texas neighbor, were chronicled in the popular multi-part HBO documentary "The Jinx" last year.

Durst was present again for Wednesday's hearing, walking haltingly into court wearing khaki pants, a light-blue collared shirt and black-rimmed glasses. He stopped briefly to look over the audience of reporters and spectators in the room.

Durst was formally charged with the Berman killing a day after HBO aired the final episode of its series, in which Durst was recorded muttering to himself off-camera: "What the hell did I do? Killed them all, of course."

Durst told authorities after his arrest that he smoked marijuana daily and was high on methamphetamine during his appearance on "The Jinx," according to court records.

Although Durst has long been estranged from his New York family and their significant real estate holdings, prosecutors have put his estimated net worth at some $100 million.

(Writing by Steve Gorman; Editing by Phil Berlowitz)