FILE - In this Nov. 7, 2016, file pool photo, real estate heir Robert Durst, right, speaks in court, his attorney Dick De Guerin, stands left, during his arraignment at the Airport Branch Courthouse in Los Angeles. A former close friend of Robert Durst has testified that the millionaire's best friend confided in him that Durst killed his first wife. Nathan Chavin said Thursday, Feb. 16, 2017, that Susan Berman told him Durst admitted killing his wife. The body of Kathleen Durst has never been found, and prosecutors say Robert Durst killed Berman to keep her from talking with police. Durst has pleaded not guilty in Berman's death and has never been charged with any crime related to his wife's disappearance. (AP Photo/Reuters, Kevork Djansezian, Pool, File)
FILE - In this Nov. 7, 2016, file pool photo, real estate heir Robert Durst, right, speaks in court, his attorney Dick De Guerin, stands left, during his arraignment at the Airport Branch Courthouse in Los Angeles. A former close friend of Robert Durst has testified that the millionaire's best friend confided in him that Durst killed his first wife. Nathan Chavin said Thursday, Feb. 16, 2017, that Susan Berman told him Durst admitted killing his wife. The body of Kathleen Durst has never been found, and prosecutors say Robert Durst killed Berman to keep her from talking with police. Durst has pleaded not guilty in Berman's death and has never been charged with any crime related to his wife's disappearance. (AP Photo/Reuters, Kevork Djansezian, Pool, File)

Los Angeles — Before she was killed, writer Susan Berman said that Robert Durst confessed to killing his wife, a key witness in the real estate scion’s murder case testified on Thursday.

Nathan “Nick” Chavin delivered the stunning testimony at a special hearing in the case against Durst, who is charged in the 2000 execution-style slaying of Berman inside her Benedict Canyon home.

Prosecutors allege that Durst killed Berman, his confidante, because he feared she was going to talk to detectives about the 1982 disappearance of his wife, Kathleen Durst.

“Susan said to me, ‘Bob killed Kathie,’ ” Chavin testified, adding that Berman told him the confession came from Durst himself.

Chavin, a longtime friend of both Durst and Berman, was hustled into court on Wednesday as a “secret witness,” flanked by bodyguards. While Durst’s trial in Berman’s murder is not likely to take place for at least another year, prosecutors had asked that Chavin testify early out of fear he might be killed before trial.

Chavin’s testimony may prove crucial, as prosecutors contend Durst made the decision to kill Berman after learning she planned to speak with investigators in New York about Kathleen’s disappearance.

Asked why he hadn’t told police of the admission earlier, Chavin said that Berman had insisted they protect Durst.

“Kathie’s dead, we can’t do anything about it,” Chavin testified Berman told him. “We have to protect Bob.”

During his testimony earlier in the week, Chavin — a New York advertising executive — said that Kathleen was afraid of her husband, even fearing he might physically harm her. Despite that fear, he testified, she never said anything to indicate her husband had been physically violent with her.

A prosecutor also asked Chavin on Wednesday if he believed Durst was involved in his first wife’s disappearance at the time that she vanished.

“No,” Chavin, 72, said emphatically.

Chavin said that he was also a close confidante of Durst, even serving as groomsman at his wedding.