Durst, who died in custody on Monday at the age of 78, was recently convicted of murdering his best friend, Susan Berman, in 2000.

Robert Durst's murder conviction will be vacated posthumously, according to an attorney who prosecuted his trial.

Durst, who died in custody Monday at the age of 78, had begun the process of appealing his September murder conviction — which found him guilty of killing his best friend, Susan Berman — before his death.

Los Angeles prosecutor John Lewin tells PEOPLE that death during a pending appeal results in a canceled conviction, due to a technicality in California that prevents convictions from being finalized until all appeals are resolved.

Lewin says that Durst's defense team filed a notice of appeal after he was found guilty, but never turned in briefs detailing their reasoning, which would have moved the appeals process along.

One of Durst's defense attorneys, Dick DeGuerin, tells PEOPLE that Durst's family was still securing appellate lawyers at the time of his death, explaining why the appeals process was still in its early stages. While DeGuerin did not plan to be a part of the appellate team, he cited Durst's poor physical health and the jury's lack of supervision during long delays in the trial as reasons one could question his conviction.

"The fact that [Durst's] death during the pendency of his appeal will cause the conviction to be vacated is an unfortunate technical rule which in no way diminishes or changes what we all know happened," Lewin says.

Neama Rahmani, a former federal prosecutor based in L.A., tells PEOPLE that the "very old" rule is common law — meaning it is based on precedent — and originates from England. It has been a point of criticism for victims of crimes, he adds.

"Some states have abandoned it but in California this remains the rule," Rahmani says. "Bob Durst is infamous for escaping justice ... so things may change with the California Legislature" — if they were to put something in code that overrules the precedent.

But as for now, "there is nothing that can be done because the court of appeal has no discretion whatsoever," he says. "There is no exception for anything."

In September, Durst was found guilty of the execution-style murder of his best friend, Susan Berman, who died in 2000. The prosecution argued during trial that Durst killed the Los Angeles author because she knew too much about the 1982 disappearance of his first wife, Kathleen Durst, whose remains have never been found.

Berman, who met Durst at UCLA in 1965, was his unofficial spokesperson after Kathleen's disappearance. Prosecutors said she helped him cover up the murder and was marked for death when she told Durst that Los Angeles and New York investigators wanted to interview her.

In October Durst was sentenced to life in prison without the possibility of parole for Berman's murder. Later that month, authorities in New York charged Durst with second-degree murder in connection with the presumed death of his first wife, Kathleen.

Kathleen's family has long hoped that Durst would tell them where he buried Kathleen, something that Lewin believes was never going to happen.

"When I interviewed him in New Orleans I really thought at the end of the interview he was very close to a confession," Lewin says, "but what I later realized, to use a football analogy: Bob Durst lets you go down the field until you get to the 5-yard line, but in actuality you are never going to get into the end zone."

"To the end Mr. Durst was unrepentant and completely unremorseful and didn't take any responsibility for his actions to the point of repeatedly continuously perjuring himself during his testimony at trial," Lewin continues. "For those reasons my sympathies lie not with Mr. Durst but with his victims and their families."

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This story originally appeared on people.com