Lawyers for the New York real estate heir Robert Durst acknowledge he wrote a note tipping off police to the location of the body of a friend he is accused of killing, according to court documents.

In a court filing last week in Los Angeles superior court, lawyers for Durst conceded he wrote the note directing police to the home where his best friend, Susan Berman, was shot point-blank in the back of the head just before Christmas 2000.

Durst, 76, pleaded not guilty to murder in Berman’s death but told a film crew the letter could only have been sent by the killer.

The revelation he sent the note was made in a joint filing by defense lawyers and prosecutors of stipulations agreed to before Durst’s trial, which is scheduled for 10 February. Attorneys said they made the concession as a strategic decision after the judge agreed to admit the evidence based on analysis by handwriting experts.

Durst’s defense had long denied he wrote the note. Attorney Dick DeGuerin said the defense would not comment on the new stipulation.

“This does not change the facts that Bob Durst didn’t kill Susan Berman and he doesn’t know who did,” DeGuerin said.

Prosecutors say Durst killed Berman because he feared his friend and unofficial spokeswoman was going to tell police what she knew about the disappearance of his wife, Kathleen, in New York in 1982.

The note sent to Beverly Hills police on the day Berman was killed has been considered a smoking gun in the case since the bombshell finale of The Jinx: The Life and Deaths of Robert Durst aired on HBO in 2015.

Durst was shown the note written in block letters that only included the address of Berman’s house and the word “cadaver”. He denied writing the note but said “only the killer could have written” it. The envelope was addressed with Beverly misspelled “Beverley”.

Film-makers then confronted him with a letter he sent Berman a year earlier that appeared to have identical handwriting, including the same misspelling.

“I wrote this one but I did not write the cadaver one,” Durst insisted. But moments later, he couldn’t tell the two apart. After a moment in which he blinked, burped and put his head in his hands, he denied being the killer.

The interview ended and Durst walked into a bathroom, unaware he was wearing a live microphone. He was heard muttering: “You’re caught! What the hell did I do? Killed them all, of course.”

One law enforcement official, who spoke on condition of anonymity because the investigation was ongoing, said analysis linking Durst to the letters was the key new evidence presented to prosecutors before his arrest.

Durst was nabbed on the eve of the broadcast in New Orleans, where he was staying in a hotel under a pseudonym and appeared to be making plans to leave the US.

After Berman’s death, Durst went into hiding in Galveston, Texas, where he disguised himself as a mute woman in a boarding house. He killed his neighbor, Morris Black, in 2001 in what he claimed was self-defense after the men struggled over a gun. He then chopped up the man’s body and disposed of it at sea.

Durst was acquitted of murder. Prosecutors claim Black was killed after he learned Durst’s real identity.

Deputy district attorney John Lewin plans to present evidence at trial that the killings of Black and Berman were part of an effort to cover up the murder of Kathleen Durst years earlier.

Kathleen Durst’s body has never been found and she was declared dead two years ago. Robert Durst, reportedly worth $100m, is considered the prime suspect in her presumed killing but has never been charged.

Witnesses who testified in pretrial hearings said Berman told them Durst acknowledged killing his wife and that she helped him cover up the crime. They also testified that Berman said if anything happened to her, Durst would be responsible.

The defense also stipulated that Durst wrote a note found in a trash can in a bedroom at the home the couple shared in Westchester county, New York, where they stayed just before Durst said he last saw his wife.

Referred to as the “dig note”, it appears to be a list including the words “town dump”, “dig” and “shovel”.