Convicted killer and New York real estate scion Robert Durst died Monday morning at a California state prison hospital facility, Fox News has confirmed. He was 78. 

Durst, heir to a real estate empire, died of natural causes around 6 a.m. PST Monday, according to his attorney Chip Lewis, and a statement from the office of Durst's longtime defense attorney, Dick DeGuerin. Lewis also told the New York Times that Durst had been taken to the San Joaquin General Hospital, where he suffered cardiac arrest. 

"Mr. Durst passed away early this morning while in the custody of the California Department of Corrections," Lewis said in a statement. "We understand that his death was due to natural causes associated with the litany of medical issues we had repeatedly reported to the court over the last couple of years."

Real estate heir Robert Durst answers questions while taking the stand during his murder trial on Aug. 31, in Los Angeles County Superior Court in Inglewood, California (Law & Crime Network via AP, Pool)

Durst has long been accused of being involved in the death of his wife, Kathleen McCormack Durst, but had not been officially charged until late last year. He was convicted in September 2021 and sentenced to life without parole for the murder of his best friend, Susan Berman. 

Durst took the stand for three weeks of testimony. A jury ultimately found him guilty of shooting Berman at point-blank range in 2000 at her Los Angeles home. 

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Under devastating cross-examination from prosecutor John Lewin, Durst admitted that he lied under oath in the past and would do it again to get out of trouble.

"‘Did you kill Susan Berman?’ is strictly a hypothetical," Durst said from the stand. "I did not kill Susan Berman. But if I had, I would lie about it."

Prosecutors share photo of Robert Durst (left), Susan Berman (middle) and Kathie Durst (right) at Robert Durst's Aug. 11 murder trial. (Fox News) (Fox News)

Durst’s health was often a topic of concern for his attorneys during the trial, when Durst had bladder cancer and his health deteriorated. He was escorted into court in a wheelchair wearing prison attire each day because his attorneys said he was unable to change into a suit. But the judge declined further delays after a 14-month pause during the coronavirus pandemic.

DeGuerin said at the time that Durst was "very, very sick" at his sentencing hearing, and it was the worst the suspect looked in the 20 years he spent representing him.

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Durst entered the courtroom with a wide-eyed vacant stare. Near the end of the hearing after Berman’s loved ones told the judge how her death upended their lives, Durst coughed hard and then appeared to struggle to breathe. His chest heaved, and he pulled his mask down below his mouth and began to gulp for air.

Robert Durst in an Inglewood courtroom with his defense attorney Dick DeGuerin in 2021. Durst was convicted in the murder of  longtime friend Susan Berman in Benedict Canyon just before Christmas Eve 2000. (Al Seib / Los Angeles Times via Getty Images)

Speaking to Fox News Digital on Monday, DeGuerin said he had learned of Durst's passing from his co-counsel and he was "not surprised."

"I had been expecting to hear of his passing just any minute. I didn’t expect him to survive the trial. He had been in very poor health."

Durst had bladder cancer, esophageal cancer, hydrocephalus of the brain, and had twice undergone operation on his cervical spine. 

"He was very ill," DeGuerin continued. "I frankly didn't expect him to survive even his testimony, much less the trial. At sentencing, he was gasping for breath. He really wasn't there."

DeGuerin and his co-counsel appealed Durst's conviction, which DeGuerin noted was still pending but "will never be resolved now." 

"This conviction is not final," DeGuerin said. "He stands as a person who was not convicted."

DeGuerin said he last spoke to his client at his sentencing in October. 

Durst had long been suspected of killing his wife, known as Kathie, who went missing in New York in 1982 and was declared legally dead.

But only after Los Angeles prosecutors proved that the motive in Berman's death was to silence her because she helped him cover up Kathie’s killing was he indicted by a New York grand jury in November for second-degree murder in his wife's death.

Robert Abrams, attorney for Kathie’s family, said in a statement on Monday that although Durst had died, "the ongoing investigation into those who helped him coverup her murder continues."

"On January 31, 2022, the 40th anniversary of Kathie’s murder, we will provide a further update," Abrams said. "In the interim, please say a prayer for Kathie and his other victims."

Robert Durst seen wrapped in blanket during trial on June 14, 2021 (POOL)

Durst was also accused of murder in Texas after shooting a man named Morris Black, who discovered his identity when he was hiding out in Galveston after Berman’s killing. Durst was acquitted of murder in that case in 2003, after testifying that he shot the man as they struggled for a gun.

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Deputy Los Angeles District Attorney John Lewin said jurors told him after the verdict that they believed Durst murdered Black in Texas and had killed his wife.

Durst discussed the cases and made several damning statements including a stunning confession during an unguarded moment in the six-part HBO documentary series "The Jinx: The Life and Deaths of Robert Durst."

Fox News' Kimberly Wagner and Rebecca Rosenberg contributed to this report, as well as The Associated Press.