Asked in March 2015 whether she believed Durst murdered Black, Criss commented: "You could see that this person knew what they were doing and that it was not a first time. The body was cut perfectly like a surgeon who knew how to use this tool on this bone and a certain kind of tool on that muscle. It looked like not a first-time job. That was pretty scary."
In early 2015, a six-part HBO documentary titled The Jinx: The Life and Deaths of Robert Durst described circumstantial evidence linking Durst to the murder of Berman, who was believed to have knowledge of McCormack's disappearance. The documentary detailed the disappearance of McCormack, Berman's subsequent death, and the killing of Black. Against the advice of his lawyers and his wife Debrah Lee Charatan, Durst gave multiple interviews and unrestricted access to his personal records to the filmmakers. The FBI arrested Durst in New Orleans on the same day as the final episode was broadcast. The documentary ended with him moving into a bathroom where his microphone recorded him seemingly saying to himself: "There it is. You're caught! .... You're right, of course. But you can't imagine. ... Arrest him ... I don't know what's in the house ... Oh, I want this ... What a disaster ... He was right. I was wrong. And the burping ... I'm having difficulty with the question ... What the hell did I do? Killed them all, of course."
A few days after a first-degree murder warrant was signed by a Los Angeles judge in relation to the Berman killing, Durst was arrested by FBI agents on March 14, 2015, at the Canal Street Marriott in New Orleans, where he had registered under the false name "Everette Ward." Durst, who had been tracked to the hotel after making two calls to check his voicemail, was observed wandering aimlessly in the lobby and mumbling to himself, having driven to New Orleans from Houston four days before.
On March 15, 2015, New York State Police investigator Joseph Becerra, long involved with the McCormack case and said to have been working closely with the FBI and Los Angeles detectives, removed some 60 file boxes of Durst's personal papers and effects from the home of Durst's friend Susan T. Giordano in Campbell Hall, New York. All of these items had been sent to Giordano for safekeeping three years prior by Debrah Lee Charatan, Durst's wife at the time. Also stored at Giordano's residence were videotaped depositions of Durst; Durst's brother, Douglas; and Charatan, all of which were related to the Black case.
On March 16, 2015, defense attorney Richard DeGuerin advised court authorities in New Orleans that his client waived extradition and would voluntarily return to California. Late that same day, Louisiana State Police filed charges against Durst for being a felon in possession of a firearm and for possession of a firearm with a controlled substance, forestalling his immediate return to California. Orleans Parish District Attorney Leon Cannizzaro commented that, in light of prior convictions that could influence Durst's sentencing, "[j]ust for those gun charges here in Louisiana, [Durst] could face up to life in prison".
After negotiations with Durst's defense team, Louisiana authorities ultimately dropped weapons charges against Durst on April 23, 2015. Durst's trial on the federal weapons charge was scheduled for September 21, 2015. DeGuerin confirmed rumors that Durst was in poor health, stating that he suffers from hydrocephalus and had a stent put into his skull two years before, as well as spinal surgery and a cancerous mass removed from his esophagus.
Durst's attorneys requested a later date for the federal weapons charge trial, saying they'd need more time to prepare after rulings on pending motions. U.S. District Judge Helen Berrigan later rescheduled the trial to January 11, 2016. On November 16, 2015, a New Orleans federal judge ordered Durst re-arraigned on the weapons charges and scheduled a hearing for December 17. When asked, Durst's attorney said only that Durst did not kill Berman, and that he wants to resolve the other charges to expedite Durst's extradition to Los Angeles to face that charge.
On December 16, 2015, prosecutors and defense attorneys told Berrigan in a joint motion that scheduling conflicts ruled out all dates before a January 11 trial date. Berrigan ultimately rescheduled the trial for February 3, 2016, and Durst changed his plea to guilty to the federal gun charge and received an 85-month prison sentence.
Durst has had a number of significant medical issues since 2015, including major surgeries for esophageal cancer, having a shunt installed in his brain for hydrocephalus, and cervical spinal fusion. When arrested in New Orleans in 2015, he was found to be in possession a variety of drugs, including the sleep aid melatonin, a muscle relaxant, and medications for high blood pressure, blood flow, and acid reflux.
On May 1, 2015, the New York Post reported that Douglas had settled litigation against Jinx filmmaker Andrew Jarecki, having confirmed that Robert was the source of videotaped depositions that appeared in the documentary. Robert's disclosure apparently violated the terms of his 2006 agreement with the Durst family, which had dispersed to him a lump sum of family trust assets. Although it was unclear whether Jarecki confirmed Robert as his source—The New York Times reported in March 2015 that Jarecki was given "unrestricted access" to Robert's personal records, including the videotaped material—the settlement paves the way for Douglas to reclaim as much as $74 million of his brother's assets, effectively freezing those assets pending court judgment. This could affect Robert's ability to pay for high-caliber legal representation without tapping into real estate or other investments. The Post reported that Douglas was "mulling his next move."
In November 2015, nearly 34 years after her disappearance, McCormack's three sisters and 101-year-old mother sued Durst for $100 million, citing his apparent role in her murder and his denial to her family of the "right to sepulcher," a New York law that grants immediate relatives access to a deceased person's body and the opportunity to determine appropriate burial. If successful, the lawsuit could deprive Durst of most or all of his inherited fortune. McCormack's brother James had attempted in October 2015 to file a wrongful death suit against Durst on behalf of his mother, but was challenged by one of his sisters, who holds her mother's power of attorney. DeGuerin said that "there is no evidence that Robert Durst had anything to do with Kathleen's disappearance. Anybody can file a lawsuit, but eventually they'll have to come with evidence." On December 7, 2015, the same family members filed a suit asking the court to freeze Durst's assets. The family's attorney, Robert Abrams, called Durst the "poster child" for why courts block defendants from disposing assets while civil lawsuits are pending. In July 2016, the McCormack family asked the Surrogate's Court in Manhattan to "declare that Kathie died on January 31, 1982, when she was murdered by her husband, Robert Durst" so the sepulcher lawsuit could proceed. The court granted the request in 2017.