Real estate heir Robert Durst (pictured during a court appearance in August) was charged on Monday in Los Angeles with first-degree murder . Robert Durst's mumblings about how he 'killed them all' provided the dramatic kick to a documentary about the millionaire's troubled life and connection to three slayings, but it was words he penned that helped lead to his arrest on a murder charge, a law enforcement official said. Analysis linking a letter Durst wrote to his friend Susan Berman a year before her death with one he said 'only the killer could have written' to point police to her body was the key new evidence in the long-dormant investigation, a police source said. Durst, 71, was charged on Monday in Los Angeles with first-degree murder in the shooting of Berman, the daughter of a prominent Las Vegas mobster, back in 2000. He could face the death penalty under special circumstances that allege he ambushed her and murdered a witness to a crime. He waived extradition in New Orleans, but authorities there charged him late on Monday with being a felon in possession of a gun because he had a revolver when he was arrested there Saturday. He was also found in possession of a small amount of marijuana. Prosecutors believed that Durst was a flight risk after the revelations of the documentary and may have been planning to head for Cuba. He was found with fake IDs in his hotel room. However one of his lawyers, Chip Lewis, told The LA Times that his client had left his Houston home for New Orleans to escape the media and that he had called daily to check in with him, asking for him by name. It was not clear how soon Durst would be returned to California. Attorney Dick DeGuerin said outside court that Durst didn't kill Berman, and is 'ready to end all the rumor and speculation and have a trial'. Presented with the two letters in the finale of The Jinx: The Life and Deaths of Robert Durst that aired Sunday on HBO, the eccentric heir 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 before the sound of running water is heard. 'What the hell did I do? Killed them all, of course.' That moment didn't just make for a captivating ending to the documentary on the eccentric life of an heir to a New York real estate fortune, it could also provide additional evidence for prosecutors. The official said the bathroom recording was not presented to prosecutors before charges were filed because detectives were still trying to determine if the recording was tampered with in any way. But legal experts said the audio and other parts of the interview could become key evidence. Durst and documentary producer Andrew Jarecki (right) examine handwriting examples  from two letters. Analysis linking a letter Durst wrote to Susan Berman a year before her death with one he said 'only the killer could have written' to point police to her body was new evidence in the investigation, a police source said . Robert Durst, far right, was escorted into Orleans Parish Criminal District Court through a tunnel entrance, in New Orleans on Monday for a court hearing to extradite him to Los Angeles to face a murder charge . 'Any statement that the defendant makes that they want to use against him, they can use against him,' said Andrea Roth, a law professor at the University of California, Berkeley. 'Even if it's sketchy, and only in context appears to make him look guilty.' Kerry Lawrence, a defense attorney in Westchester County, New York, said Durst's lawyers will have to try to explain away his comments, perhaps dismissing them as a joke. 'Prosecutors would argue it was a candid moment of self-reflection, and I assume will argue that he knew he was still being recorded, and this was either said in jest or he was being facetious or sarcastic or was being provocative,' Lawrence said. 'I don't think it's quite the smoking gun.' Durst — still worth millions despite his estrangement from his family, whose New York real estate empire is worth about $4 billion — has maintained his innocence in three killings in as many states. When Durst approached the filmmakers and agreed to go on camera, against the advice of his lawyers, he had already weathered one murder case, winning an acquittal in a gory Galveston, Texas, dismemberment case by claiming he shot his neighbor in self-defense. He was still suspected in the killing of Berman, whose father was a Las Vegas mobster associated with Bugsy Siegel and Meyer Lansky, and the disappearance of his wife, Kathleen, who was declared dead long after she vanished in New York in 1982. Susan Berman was found shot execution-style outside her home in LA in 2000. Her friend, Robert Durst, was charged with her murder on Monday . Kathleen's brother, Jim McCormack, told Today on Tuesday that he believed Durst's confession was genuine and an admission that the 71-year-old had killed his sister decades before. Mr McCormack said: 'The revelation was like something we‘ve been waiting for 33 years.' He added: 'I believe that Bob will somehow have an epiphany of conscience, contrary to the advice of lawyers. 'I think he’s about ready to say, ''You know, enough is enough. This is what Kathy would want and this is what I’m going to do.''' Susan Berman, 55, was shot once in the back of the head at her home near Beverly Hills shortly before New York investigators planned to question her about Kathleen Durst's disappearance. The documentary showed filmmaker Andrew Jarecki confronting Durst with a copy of an anonymous letter that alerted Beverly Hills police to look for a 'cadaver' at Berman's address. Durst offered that whoever sent it was 'taking a big risk. You're sending a letter to police that only the killer could have written.' Then, in the final episode, Jarecki revealed another envelope, which Durst acknowledged mailing to Berman, that has similar writing in block letters and also misspelled the address as 'Beverley.' 'I wrote this one but I did not write the cadaver one,' Durst said. But when shown an enlargement of both copies, Durst couldn't distinguish them. New York defense lawyer Michael Devorkin said the surprising thing was that police never unearthed the letter to Berman that filmmakers got their hands on. 'Even if Durst wasn't the prime suspect, you would think they would have been looking through all her papers to see if the person who killed her had ever written her a letter,' Devorkin said. 'Finding the letter was pure good fortune.' With the bathroom recording immediately following the confrontation over the two handwriting samples, prosecutors have strong evidence, said Devorkin, who handles white-collar criminal cases. 'How often do you have a Perry Mason moment to end your documentary?' he said. Robert Durst's first wife, Kathleen McCormack (pictured left),  has been missing since 1982. Her brother, Jim McCormack, said on Tuesday that following the HBO show he hoped Durst would have an 'epiphany of conscience' and tell them what happened to his sister . Robert A. Durst's attorneys, including Dick DeGuerin, center, and William P. Gibbens, left, speak after leaving court in New Orleans on Monday. DeGuerin said  Durst didn't kill Berman, and is 'ready to end all the rumor and speculation and have a trial'
Durst, 71, was charged on Monday in LA with first-degree murder in the shooting of Susan Berman, daughter of a prominent Las Vegas mobster . He could face the death penalty under special circumstances that allege he ambushed her and murdered a witness to a crime . The eccentric heir was charged in New Orleans with being a felon in possession of a gun and also had a small amount of marijuana .