Durst, 60, and Morris Black, 71, were neighbors. Durst claims Black came into his apartment, grabbed a gun that Durst had hidden and pointed it at him. Durst then said that they struggled over the gun before it went off, killing Black accidentally.
At Durst's two-month trial, the jury's not-guilty verdict, after five days of deliberation, shocked everyone – including Durst himself.
But lead investigator, Det. Cody Cazalas, says he's rarely had a more clear-cut case of murder. "I believe that he probably walked up behind him and shot him in the back of the head," he says. "There was nothing to suggest self defense … He never said self defense until after the defense attorneys got the case."
What made Durst's claim of self-defense even harder to believe was that after the shooting, instead of calling the police, he chopped up Black's body, loading the parts into plastic bags and dumping them into Galveston Bay.
"I think he assumed that the tide would take the bags on out to sea. But instead, the bags just stayed right there by the pier," says Cazalas. "He didn't panic. Everything he did was cold and calculating."
The jurors, who were widely criticized for the acquittal, said it proved to be a most difficult decision. But they say they had no choice. While they knew Durst had cut up the body, they weren't convinced he had actually committed premeditated murder.
Is Durst a cold-blooded killer with a string of victims over more than 20 years? Or is he somehow a victim himself? Correspondent Erin Moriarty talks to Durst's closest friends and his defense psychiatrist, Dr. Milton Altschuler – a therapist who, with Durst's permission, speaks out for the first time.
The Durst fortune, valued at more than $2 billion, is in the same league as Donald Trump's fortune. And it's certainly more than enough for the best legal defense that money can buy.
His high-powered defense team - Dick DeGuerin, Mike Ramsey and Chip Lewis – say that early on, they had difficulty communicating with Durst. So they hired Dr. Altschuler, a well-known Houston psychiatrist, to find out why.
Altschuler says he met with Durst almost on a weekly basis, and spent more than 70 hours examining him. His conclusion: Durst suffers from a form of autism called Asperger's syndrome. It's a fairly uncommon disorder that leaves a victim's intellect intact, but limits his ability to interact socially.
"Emotion is very difficult to him. He doesn't know what happy is," says Altschuler. "He can feel it, but almost as if he were feeling it as we would feel fingers through a glove. It's very dulled, at best, to him … His whole life's history is so compatible with a diagnosis of Asperger's disorder."
The jury apparently bought it. They were convinced that Durst, in a panic, dismembered Black's body.
"It would have been an explanation for some of the inappropriate -- and obviously, it was inappropriate to dismember a corpse -- behavior that Bob went through," says Ramsey.
If you travel nearly 2,000 miles southwest of New York City, the road ends at the Gulf port of Galveston, Texas.
Durst says he came to Galveston in late 2000 to get as far away as he could from New York tabloid reports that were tying him to another mystery – the 1982 disappearance of his first wife, Kathie.
"I have no reason to believe that she isn't dead and that this wasn't a homicide," says Jeanine Pirro, the district attorney of Westchester County, N.Y., who is actively investigating the case. "We want to talk to Bob Durst and he won't talk to us. There's no one who knows more about what happened to Kathleen, and what her last actions were than Robert Durst. And he won't talk to us."
In the winter of 1982, Kathie Durst, who'd been married to Robert for 11 years, disappeared. Strangely, Durst waited several days before notifying either the police or his wife's family.
Did he sound worried? "No, it was almost casual," recalls Kathie's brother, Jim McCormick. "And almost rushed, to get the phone call out of the way."
"He's a very odd person," says Kathie's close friend Ellen Strauss. "He was tossing out her things and trying to rent her apartment – immediately after disappearing."
Strauss is so convinced that Durst killed her friend that she's been collecting evidence for years, and storing it in a safe deposit box -- even sharing it with investigators.
"I keep certain items that can't be reproduced. Every scrap of paper that I wrote in 1982," she says. "I made a promise, not that I would avenge her, but that I would get to the bottom of it. That's what friends are for."
Kathie was just 19 when she left home in suburban Long Island for the bright lights of New York City.
"The apartment she was living in was owned by the Durst Organization, and Bob was apparently some collector of rents," says McCormick.
Kathie and Robert got along instantly, and within two years, they married.
"She was crazy about him," says Strauss. "He was quiet and there was that dark side to him. He was always dark and brooding and some women find that attractive."
Plus, there was the lifestyle Durst's world-class fortune could buy: going to discos like Studio 54, star-studded parties and exotic travel all over the world.
While Durst worked in the family real estate business, Kathie decided to go to medical school. But her friends say that did not make her husband particularly happy.
"He was very tight with money in terms of going to school. She had to come up with ways to do things on her own," recalls Strauss. "In spite of the fact of being married to Bob Durst, he was not generous."
Friends say Durst wouldn't help cover Kathie's medical school, and sometimes wouldn't even pay for home repairs.
The marriage grew strained, and by 1981, most of her friends knew there were serious problems.
"Kathie was being abused by Bob physically. She always said that if anything ever happens to me, look to Bob," says Strauss.
"The one time I saw the physical violence was when he was impatient to leave my mom's house in New Hyde Park," recalls McCormick. "He turned around and walked over and grabbed her by the hair, and pretty much yanked her right off the couch … Just kind of pulled her. I should have ripped his face off."
In January 1982, Kathie suddenly disappeared. Her friends say it was after a confrontation with her husband, but Durst tells a very different story. He says they had dinner together that night and then he dropped her off to catch a train back to New York City. That's the last time he says he ever saw her.
"It sickened him that he's been suspected of killing a woman that he loved very much," says Durst's laywer, Dick DeGuerin, who claims his client had no reason to kill his wife. "He has her wedding picture in his cell in Galveston."
"There were several people interviewed by police at the time who gave written statements that saw her after Bob had last seen her," adds Durst's lawyer, Mike Ramsey.
But sources in the investigation have told 48 Hours they question the credibility of some of those witnesses. And, there was another issue: the troubles in the Durst marriage were escalating.
The police have never found Kathie's body – and don't have enough evidence so far to charge anyone with her death. But Pirro says her office is not giving up: "You don't need a body in criminal case. It's a lot harder without a body, but that's not going to stop us."
In the freewheeling beachfront bars of Galveston, Texas, you'll hear another strange story about Bob Durst -- that when he first came here from New York to hide out from the media, he came disguised as a woman.
His cross-dressing made headlines during the Morris Black murder trial. And his attorneys even used it as part of their defense strategy.
"Why did a rich guy end up in Galveston wearing a wig, masquerading as a woman, and hiding from the world," asks Ramsey, Durst's attorney. "Well, we have an answer for that. It's a complex answer. It has to do with a psychological disorder."
According to Altschuler, it's a psychological disorder that helps to explain why Durst panicked and chopped up Black's body in the Texas murder case.
Altschuler says the disorder is called Asperger's syndrome, the rare form of autism that he says makes Durst act inappropriately in stressful situations.
But Durst's oldest friends in life know a very different person. "People really have the wrong impression of Bob," says Stewart Altman, who flies regularly to visit Durst at the Galveston jail.
Altman has been Durst's friend and at times legal advisor for 40 years. He and his wife, Emily, are also speaking out for the first time. "He's just a regular guy who happens to have a lot of money," he says. "I don't see why people should hold that against him."
Altman and Durst met in high school in the upscale New York suburb of Scarsdale, where Durst – the firstborn prince of New York real estate royalty – struggled to make friends.
"Socially, Bob was not a great success," recalls Altman. "I always knew Bob had these problems relating to other people."