The death of Robert Durst, the tragic, creepy and ridiculously wealthy New Yorker who was cast out of his massively rich family’s real-estate empire for urinating into a waste-paper basket, leaves an enduring mystery buried, likely forever: What happened to Kathie Durst?

In his 78 years on earth, Durst lived like a demented pauper, sometimes dressed as a mute woman, roaming the country on an alleged killing spree. He was a suspect in his wife Kathie’s 1982 disappearance from their Westchester County home and was tried and acquitted in 2003 on grounds of self-defense for the gunshot slaying and dismemberment of an elderly neighbor in Galveston, Texas, two years earlier, which he freely admitted to carrying out.

After that killing, he lived for a time on the run, carrying tens of thousands of dollars in cash, only to be arrested for shoplifting a sandwich. But he was as lucky as he was cheap. Robert proved he was covered in Teflon, waltzing out of the Texas courthouse, a free man.

His freedom unnerved his own younger brother, Douglas Durst, whom Robert had hated since his father installed him as the head of the New York City-based Durst Organization in 1994 after Robert’s bizarre and gross behavior forced him to pass him over.

“I came back from vacation and I was putting my hand into the wastepaper basket and it was covered by liquid. It was urine,” Douglas told me in a rare interview in 2015. Ick.

“It was I who asked the staff, and they said my brother did it frequently,” said

Douglas, now 77. He maintains his bro tried to kill him, too.

“Given the opportunity, he would kill me, yes.

“If that makes me a pussy, then I’m a pussy,” he said. Yikes.

He was referring to an incident in 2001. As I reported exclusively, Robert was seething with rage over his little brother’s ascent in the family business. In the midst of running from the law, he attempted to even the score.

Robert drove to his sibling’s house in Katonah, NY, and parked his car. He was armed and, Douglas believes, ready to kill.

But he drove off without incident.

This prompted Douglas to hire a bodyguard – which led Robert to trash him as a “pussy” in a taped deposition he gave after his capture, which was excerpted in the HBO docuseries “The Jinx: The Life and Deaths of Robert Durst.”

The unmanly slur clearly stung.

It seems the Durst Family Drama enraged Robert, who has long exhibited sociopathic or psychopathic behavior, even as he denied involvement in doing away with Kathie. In the documentary about his life, he described his father, Seymour Durst as distant and cold, and claimed to be traumatized after, at age 7, he witnessed ”Mommy” – Bernice Durst — either jumping or falliing to her death from their Westchester house’s roof.

Douglas insists none of this is true.

“My father loved him,” Douglas told me. “Actually, he was my father’s favorite.”

He also said that on the he night Bernice Durst died in 1950, Robert was not at the family’s house but rather at a neighbor’s place, along with Douglas and two other siblings.

On Monday, he issued a brief statement about his brother, who died naturally from a litany of health woes inside a California prison.

“Bob lived a sad, painful and tragic life,” Douglas stated. “We hope his death brings some closure to those he hurt.”

But what about Kathie?

Westchester authorities indicted Robert Durst in November for the murder of Kathleen Durst nearly 40 years ago. This came just days after he was sentenced to life in prison without parole for the 2000 murder of close pal Susan Berman in Los Angeles. Prosecutors maintain that he shot Berman to death at point blank range to prevent her from telling what she knew about Kathie’s slaying. Finally, it appeared Robert Durst would face the music.

But Durst died before this could happen. Kathie’s remains were never found. There are no known witnesses to her demise.It seems justice delayed is justice denied.

It seems Robert Durst got away away with murder.