Confronted with new evidence by the makers of a documentary about his life, the troubled millionaire blinked, burped oddly, pulled his ear and briefly put his head in his hands before denying he was the killer.
Then he stepped away from the tense interview and went to the bathroom, still wearing the live microphone that recorded what he said next.
"There it is. You're caught!" Durst whispered to himself before running the tap water. "What the hell did I do? Killed them all, of course."
It also may have given police and prosecutors the evidence they needed to close the long-cold case of a mobster's daughter. Susan Berman was felled by a bullet to the back of her head as investigators prepared to find out what she knew about the disappearance of Durst's wife in 1982.
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In Louisiana, Durst was rebooked on charges of being a convicted felon in possession of a firearm, and possession of a weapon with a controlled dangerous substance - a small amount of marijuana.
The charges came after two years of investigation and allege he lay in wait with a gun and murdered a witness, special circumstances that could carry a death sentence if prosecutors decide later to pursue it.
Durst, 71, who was arrested at a New Orleans hotel on the eve of Sunday's final episode of the documentary, agreed Monday to face trial for the murder of Berman, who had vouched for him in public after his wife vanished.
The makers of "The Jinx: The Life and Deaths of Robert Durst" said Durst had waved off his lawyer's advice to stay quiet before granting them two lengthy interviews. They also say he knew he was being recorded throughout, and that they shared any evidence they gathered with police long before broadcasting the film on HBO.