“We became fast friends,” Mr. Durst said during courtroom testimony in Galveston, Tex. “We were never boyfriend and girlfriend.”

Mr. Durst counted on Ms. Berman to shield him from the press when his wife’s sudden disappearance generated tabloid headlines in New York. He walked her down the aisle when she married at the Hotel Bel Air in Los Angeles in 1984.

He left the family business in 1994 after his father, Seymour Durst, appointed his younger brother Douglas to take control of the Durst Organization. He has been estranged from his family since then — Douglas is expected to testify for the prosecution in Los Angeles — and for years led a peripatetic life, moving restlessly among California, New York and Texas, even as he became a suspect in three murders.

But it was Mr. Durst’s own hubris that brought his freewheeling ways to an end.

Beginning in 2010, he agreed to participate in the documentary — “The Jinx: The Life and Deaths of Robert Durst” — about his life and the murder allegations, which was eventually broadcast on HBO in February and March 2015.

His friends and lawyers had advised him not to participate for fear of antagonizing prosecutors.

But Mr. Durst told The New York Times he thought there was “no reason I shouldn’t say anything I want to anyone I want,” because it was unlikely that any prosecutor would undertake a “budget-busting” investigation for a couple of cold cases.

In “The Jinx,” Mr. Durst said Ms. Berman contacted him in October 2000 saying the authorities wanted to talk to her about his first wife. In quick succession, he married his current wife, Debrah Lee Charatan, and fled New York, renting modest apartments in Galveston and New Orleans while posing as a mute woman.

In December of that year, Ms. Berman’s body was found in her Los Angeles home, the back door open and her dogs running loose.