LOS ANGELES - A so-called secret witness in the Los Angeles murder case against New York real estate heir Robert Durst was revealed Wednesday as a longtime friend of the millionaire and the woman he is accused of killing.

New York advertising executive Nathan "Nick" Chavin entered a courtroom through a back door with a personal security detail for his protection.

Chavin, 72, said he once considered Durst his best friend and thought the feeling was mutual with one exception: Durst was even closer with their friend Susan Berman, whom Durst is accused of fatally shooting in 2000 at her Los Angeles home.

Chavin was called to testify in a rare proceeding to record testimony from a few elderly witnesses and those who fear for their safety and may not be alive to testify at trial.

In order to protect Chavin, his name was only provided to the defence two weeks ago - after he had travelled from his New York home to an undisclosed location in California - and not released publicly until he took the stand.

Prosecutors have suggested that with Durst's estimated $100 million fortune, he could have witnesses knocked off. The defence said that suggestion is absurd and have pointed to Durst's frail condition and the fact he's in jail where his phone conversations are recorded.

Chavin did not offer any testimony connecting Durst to Berman's killing before his testimony concluded for the day, but Deputy District Attorney John Lewin alluded earlier to incriminating testimony from the witness that could "bury" Durst.

Chavin described watching Durst's first marriage deteriorate before his wife, Kathleen, mysteriously disappeared in 1982

Kathie Durst, as she was known, had confided in Chavin that she feared her husband.

"She said she was afraid of him," Chavin said. "She never said he hurt her."

He told of two violent incidents Durst described to him, including one that involved kicking a man in the head who had flirted with his wife.

"The guy pissed him off," Chavin said and he noted that Durst never showed any regret for the incident or distress after being sued.

In another incident, Durst said he had run over a woman police officer in the San Francisco Bay Area while creeping through traffic.

Chavin asked why he wasn't in jail.

Durst replied: "What's she going to do, go to her superiors and say, 'He ran over me at 1 mph?"' Chavin said. "I think he did it in a prankish way."

Chavin said he did not think Durst was responsible for his wife's disappearance at the time, but that line of questioning was interrupted by the court's recess for the day. He returns to the stand Thursday.

Prosecutors contend that Durst killed Berman because he thought she was going to talk to police about his wife's disappearance. Berman had acted as his unofficial spokeswoman during that time.

A woman who works for Chavin was questioned earlier in the day about statements she made about Durst allegedly discussing needing an alibi for his whereabouts around the time of Berman's death, which happened close to Christmas.

Susan Giordano, 50, who described Durst as her best friend and said he promised to provide money so she's set for life, seemed confused by the questions.

A transcript of an interview with Lewin was displayed in which she acknowledged telling investigators that she thought it was odd Durst needed someone to say they were with him around the time of Berman's death if he didn't kill her.

Giordano said Wednesday she has misunderstood what investigators were asking her.

Giordano said she loves Durst and has visited him several times in jail and speaks with him regularly. So far, he's given her $350,000, which she described as a combination gift and loan, though there's no formal repayment agreement. She said she's paid back $2,000.

Despite planning to use his funds to purchase a "love nest" where the two can live on the same property, she said they are friends only and not romantic.

Giordano was called for an unrelated matter about dozens of boxes of Durst's documents that she stored in her parent's basement next door to her New York home. Police seized the boxes as evidence and lawyers are fighting over whether the contents can be searched.

Lewin veered widely from that subject while grilling Giordano. The defence repeatedly objected to the questioning, saying it was beyond the scope of what they had agreed to.

Judge Mark Windham allowed Lewin to press Giordano to show inconsistencies from previous statements to investigators in his efforts to show she was trying to protect Durst.

In a preview to testimony that could come from Chavin, Lewin asked whether Durst and his defence team were worried about what his longtime friend would say.

"Have Mr. Durst's lawyers expressed concerns to you that Nick Chavin might bury him?" Lewin asked. "Have you ever said to Nick that Bob is sick to death that Nick is going to say something to the prosecution that is bad for him?"

Giordano said "no" to both questions.