Real estate heir Robert Durst appears in a criminal courtroom for his trial on charges of trespassing on property owned by his estranged family, in New York, in this December 10, 2014 file photo. [Photo/Agencies]

NEW ORLEANS - Robert Durst couldn't explain away the similarities between his handwriting and a letter he said "only the killer could have written" that alerted police to his friend's shooting 15 years ago.

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."

That moment didn't just make for a captivating finale to a six-part documentary on the eccentric life of an heir to a New York real estate fortune.

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.

Los Angeles prosecutors filed a first-degree charge against Durst on Monday that could trigger the death penalty.

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.

Authorities didn't immediately know whether prosecutors would try to keep Durst in Louisiana on those charges before he is sent to Los Angeles.

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.