Long Island’s most notorious serial killer will help the FBI figure out what makes his sick mind tick — part of his chilling plea deal in eight cold-case slayings, officials said Wednesday.

The stipulation that Gilgo Beach serial killer Rex Heuermann, 62, will sit down with the agency’s Behavioral Analysis Unit comes along with a promise that he’ll serve three life sentences without the chance of parole when he goes back in front of the judge on June 17 for sentencing in the gruesome murders of eight sex workers dating back to 1993.

“They’re going to interview the defendant, gain insight into his motivations and background as sort of an academic and scientific exercise,” Suffolk County District Attorney Ray Tierney told reporters.

“Those are clinical interviews. Those aren’t investigative interviews,” he said. “I believe that they’re going to limit that to just …. what he pled guilty to and just gain insight, so they can gain insight going forward and knowledge to move forward don new cases.”

Heuermann’s lawyer, Michael Brown, would not discuss the extent of the FBI deal, other than to tell Judge Timothy Mazzei in court that “he will cooperate with and answer truthfully, cooperating with the FBI.”

The agency’s behavioral analysis unit focuses on investigating the psychology of the criminal mind, and has cut similar agreements with other high-profile serial killers in the past.

Notorious serial killer Ted Bundy worked with the FBI and local cops to identify Gary Ridgway, the so-called Green River Killer, by providing insights into his criminal fetishes.

Bundy, who was convicted in 1976 and confessed to more than 30 murders, became obsessed with Ridgway and heled the FBI create a profile of the killer, according to a 2022 Fox News report.

Edmund Kemper, believed to be the inspiration behind the fictional “Buffalo Bill” killer in the hit flick “Silence of the Lambs,” was grilled by the feds after his arrest in 1973.

Kemper, who killed more than a half dozen women starting when he was just 15, including his own grandmother and mother, agreed to be interviewed to provide insight into the sick criminal mind.

Retired NYPD Sgt. Joseph Giacalone, an adjunct professor at John Jay College of Criminal Justice, said he thought the FBI partnership with Heurmann might aim to get to the root of what turned him into a monster.

“It’s a great idea in regards to trying to get into the mindset of how somebody gets to the point that he did, and I guess looking for any indication if there other potential victims out there, we may not get to that point,” he told The Post.

“But it’s about the idea of studying the behavior whether it’s biological or it stemmed from his environment or experience.”

Giacalone, former commanding officer of the Bronx cold case squad, said he believes there may be more victims out there.

“Absolutely. I think the chances are very high,” he added. “There’s a 12 or 13 year gap where everything just stopped. You have somebody who has been doing it since 1993, I think it’s hard to fathom that he didn’t murder other people.”