Ms. Charatan, like Mr. Durst’s lawyer, had advised him against participating in an HBO documentary, “The Jinx: The Life and Deaths of Robert Durst,” which concluded with what seemed to be Mr. Durst’s whispered confession, caught on a recording. “What the hell did I do?” he said. “Killed them all, of course.”

Image Robert A. Durst Credit... David J. Phillip/Associated Press

In January, before the series was broadcast, Mr. Durst said in an interview, “My wife, Debrah Charatan, is extremely formidable and always has a strong opinion about what I do.”

Investigators in Los Angeles want to talk to Ms. Charatan about Mr. Durst’s whereabouts and actions before and after they were married. They believe that Ms. Charatan, like Ms. Berman in Los Angeles, knew some of Mr. Durst’s secrets. But Ms. Charatan is protected by law from being compelled to testify against her husband.

Ms. Charatan could waive the spousal privilege to discuss what she learned about Mr. Durst. But he could legally block her from disclosing any confidential communications, Dan Bookin, a criminal defense lawyer in San Francisco, said.

The Los Angeles district attorney declined to comment about Ms. Charatan.

Ms. Charatan, 58, who is described as a keen-eyed investor with very sharp elbows by those who know her, has long refused to talk about Mr. Durst, and she declined to be interviewed for this article. She has her admirers among developers like Larry Silverstein and the parking magnate Jerry Gottesman.

“I always found dealing with Debbie to be very straightforward,” said Robert A. Knakal, the chairman of real estate investment sales at Cushman & Wakefield in New York. “She seems to be doing very well as an investor now.”