Real estate heir and long-time murder suspect Robert Durst has been arrested after he appeared to admit to multiple killings for a HBO documentary series. Durst, 71, was arrested on Saturday after he inadvertently admitted to murder whilst shooting The Jinx: The Life and Deaths of Robert Durst.

Robert DurstRobert Durst [L] has been arrested after appearing to admit to murder during the filming of a HBO documentary [Getty/James Nielsen]

Durst was heard to say "What the hell did I do?...Killed them all of course" into a microphone that he erroneously assumed was turned off. 

Durst was suspected of killing his writer pal Susan Berman in Los Angeles shortly before Christmas 2000. His first wife Kathie Durst went missing after the pair began talking divorce and her body was never found. Durst admitted to killing and dismembering elderly Texas neighbour Morris Black, whose body parts were found in Galveston Bay. He was eventually acquitted of murder after claiming that he killed the man in self-defense.

More: John Oliver goes after elected state judges on Last Week Tonight

Durst's new confession came after he was presented with damning evidence in the form of a recently discovered letter from himself to Berman. The handwriting matched an anonymous letter directing cops to Berman's body in 2000.

"There it is. You're caught," Durst said after walking off the set of the HBO documentary and into a bathroom,. "What a disaster."

A source close to the Los Angeles District Attorney's Office said they received the letter and other "compelling evidence from the HBO team" prior to Durst's arrest. 

Last year, Mr Durst was acquitted of trespassing at his brother's and nephew's homes in Hell's Kitchen, New York. He pleaded no contest. He was also fined $500 for urinating in a CVS store in Houston in July 2014.

More: John Oliver returns with savage takedown of pharmaceuticals companies