Robert Durst must pay a private investigator he’d stiffed $165,000 after a judge determined that the killer real estate scion failed to prove his claim that the bill was excessive.

Durst hired New York-based T&M Protection Resources two weeks after he was arrested in 2015 for the murder of his friend Susan Berman.

The 75-year-old is currently jailed in Los Angeles for killing Berman to prevent her from talking to prosecutors about his involvement in the 1982 disappearance of his wife Kathie.

In 2004 Durst was acquitted of other murder charges in Texas after testifying that he shot his Galveston neighbor in self-defense and then dumped the body.

T&M Protection sued last year after Durst contested the $130,000 bill for 500 hours of field work and digital research into the events surrounding his capture.

Late Wednesday Justice John Kelley ordered Durst to pay $165,000, which includes interest, finding that he didn’t specify in response to the suit what items on the firm’s invoices were excessive.

When Kelley heard arguments on the payment dispute last month he admitted to knowing nothing about the notorious killer who was caught on a hot microphone for a 2015 HBO documentary muttering, “What the hell did I do? Killed them all, of course.”