The prosecutor leading the case against Robert Durst repeatedly questioned the New York real estate scion’s credibility and accused him of lying during the trial for the California murder of his best friend.

Deputy District Attorney John Lewin repeatedly questioned Durst about his lies during Tuesday’s cross-examination in connection with the 2000 death of Susan Berman. Durst said he hadn't lied — at least up to that point — during his five days of ongoing testimony in Los Angeles County Superior Court.

Under cross-examination from Lewin, who relished the prospect of grilling Durst and prepared a 200-page outline for questioning, the multimillionaire acknowledged there are some acts he would never come clean about.

ROBERT DURST TESTIFIES HE'D LIE IF HE NEEDED TO ON STAND IN SUSAN BERMAN MURDER TRIAL

"If you’ve said you’ve taken an oath to tell the truth but you’ve also just told us that you would lie if you needed to, can you tell me how that would not destroy your credibility?" Lewin asked.

"Because what I’m saying is mostly the truth," Durst said. "There are certain things I would lie about, certain very important things."

ROBERT DURST TESTIFIES ABOUT LAST WEEKEND HE SAW WIFE KATHIE BEFORE SHE VANISHED

Durst said he would never admit to killing Berman — even if he had done so.

"'Did you kill Susan Berman?' is strictly a hypothetical," Durst said. "I did not kill Susan Berman. But if I had, I would lie about it."

Durst, 78, has pleaded not guilty to murder in the point-blank shooting of Berman, his longtime confidante, in her Los Angeles home. Durst said he found a lifeless Berman lying on a bedroom floor when he showed up for a planned visit just before Christmas in 2000.

Prosecutors say Durst silenced Berman as she prepared to speak with New York authorities about the disappearance of his wife, Kathie, in 1982 and how she provided a false alibi for him. They also say he murdered a neighbor who discovered his true identity when he was hiding from authorities in Galveston, Texas, in 2001.

Robert Durst has never been charged with a crime in his wife’s disappearance and has denied killing her.

He was acquitted of murder in Morris Black’s death after he testified he fatally shot the man during a struggle for a gun. He was convicted of destroying evidence for chopping up the man’s body and tossing it out to sea.

If he had killed his wife and murdered Black, Durst said he wouldn't admit those crimes.

Testifying at trial is incredibly risky for a defendant, and most lawyers won't put their clients on the stand. Durst's testimony Tuesday showed that a history of lies and inconsistent stories had made him vulnerable.

"You don’t just make up lies for the sake of lying," Lewin said. "You lie in particular when there is a reason for you to lie. And, generally speaking in this context, when it relates to incriminating evidence, correct?"

Durst agreed.

In questions from his own lawyer, Durst said he had not confessed to any killings when he was captured speaking to himself on a live microphone after filming a documentary about his life and the deaths of people close to him.

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In the climactic scene of "The Jinx: The Life and Deaths of Robert Durst," he could be heard in a bathroom muttering: "What the hell did I do? Killed them all, of course."

Durst, who had just been caught on video in a lie about a note directing police to Berman’s "cadaver," explained that the mic hadn't captured his full thought.

"What I did not say out loud or, perhaps I said very softly, is: ‘They’ll all think I killed them all, of course," he testified.

Durst is due back in court Wednesday when Lewin’s cross-examination is expected to continue. 

Fox News' Michael Ruiz and the Associated Press contributed to this report.