Could one letter finally put the billionaire many believe has gotten away with murder behind bars?
The new evidence was shown publicly for the first time Sunday night in the six-part HBO documentary, The Jinx: The Life and Deaths of Robert Durst.
Cross-dressing Durst was the black sheep in one of New York's wealthiest families, The Durst Organization, which manages One World Trade Center.
His beautiful wife, Kathleen McCormack, vanished without a trace in 1982 and has yet to be found.
Then, Durst's close friend, Susan Berman, was found shot to death execution-style at her house in Los Angeles shortly before she was to be questioned about what, if anything, she knew about Kathy's disappearance.
Police have long suspected that Durst was the author of an anonymous note sent to the Beverly Hills Police Department alerting them to a body at Susan Berman's home, but, they've never been able to prove that Durst was the author of that note, possibly until now.
In the documentary, Susan Berman's stepson showed a producer a 1999 letter from Durst to Berman that he said he just discovered. The block lettering appeared to be very similar to the lettering on the note sent to police. And, Beverly Hills was misspelled on both notes.
Matt Birkbeck is the author of A Deadly Secret about the Durst case.
He told INSIDE EDITION, "He has already said on camera that he had nothing to do with Susan Berman's murder. And now you've got this letter, which if they can link up to the original cadaver letter, it means that he was lying and that he knew about it and in all likelihood he killed her."
Now, the District Attorney in Los Angeles has reportedly reopened the investigation into Berman's death.
Last week, Durst told The New York Times that he had no idea who killed Susan Berman or what happened to his first wife.
INSIDE EDITION spoke to Berman's friend, Barbara Stabiner.
She told INSIDE EDITION, "A mad man is on the loose."