When disgraced crypto kingpin Sam Bankman-Fried left court last December, free on $250 million bail, he was escorted to his vehicle by a boulder of a man in a tailored suit, thinning hair slicked back above an impeccably groomed mustache. In the months since, the rock has been practically glued to the former tech wunderkind, showing up in picture after picture escorting Bankman-Fried to and from his many court appearances.

He may be built like a linebacker, but he’s a far cry from a bodyguard. A former N.Y.P.D. detective, Jimmy Harkins, 59, is a legendary private investigator who’s pounded pavement and turned up dirt in some of the most notorious cases in New York criminal history, helping defend Epstein crony Ghislaine Maxwell, mobster John Gotti Jr., and taking on other infamous clients, such as O. J. Simpson. Now the old-school bruiser is working for a guy whose only weapon is a V.P.N. key.

Harkins escorts his latest client, Sam Bankman-Fried, to arraignment proceedings at the Manhattan Federal Court in New York.

Bankman-Fried’s criminal case stems from last year’s chaotic collapse of FTX, the crypto-currency exchange he ran from a penthouse apartment in the Bahamas. Prosecutors allege that Bankman-Fried was at the top of a wild scheme to defraud investors out of billions while spreading the money around to everything from personal bank accounts and shell corporations to nonprofits and political campaigns—and so far they’re bringing a strong case.

Last Friday, District Judge Lewis Kaplan revoked Bankman-Fried’s hard-won bail, sending him to jail in New York’s notorious Manhattan Detention Complex (also known as “the Tombs”) after prosecutors said he had repeatedly attempted to influence witnesses. When Bankman-Fried arrived at the hearing on Friday, Harkins was once again on his tail, shepherding the frazzled-looking founder in and out of the courtroom like an oversize and overqualified assistant.

In a phone conversation on Tuesday, Harkins declined to comment on the case. Bankman-Fried’s attorney Mark Cohen did not respond to a request for comment. (Cohen and his partner Christian Everdell also advised Maxwell in her case connected to Epstein’s sex-trafficking network, for which she is now serving a 20-year sentence in prison.) Still, plenty of people in Harkins’s orbit were happy to talk about the man behind the suit and ’stache.

“I’ve got Jimmy working on a number of cases for me,” says New York criminal-defense attorney Jeffrey Lichtman, who worked with Harkins on the Gotti case and also represented the Mexican drug lord Joaquín “El Chapo” Guzmán. “He’s probably the last of an old breed. He’s very competent, he’s hardworking, he’s dependable, and he gets you the information you need.”

Harkins, second from left, during a 1988 police ceremony covered by the Staten Island Advance newspaper.

That information can be, well, anything. If it’s evidence that helps the client, it’s Harkins’s job to find it. In 1997, for instance, Harkins turned up an ancient guest ledger from a New Jersey hotel that helped Michael “Mikey Cigars” Coppola, of the Genovese mob family, beat a murder charge.

“He doesn’t get scared easily,” Lichtman says. “He’s not a delicate flower when it comes to putting his nose in places that are not the safest and easiest places to be in. Jimmy does whatever he has to do to get the job done. He’s ethical, but he’s also aggressive and relentless.”

If Harkins is on the case, “any prosecutor knows that they’re up for a good fight,” bail bondsman Ira Judelson tells me. Judelson, who provided bail for Harvey Weinstein, former I.M.F. head Dominique Strauss-Kahn, and many other high-profile defendants, said he’s worked with Harkins for decades. “He’s one of those hands-on, dig-deep, get-dirty guys,” Judelson says. “He’ll fly to Florida, he’ll fly to St. Louis, he’ll fly to Vegas, all to dig up … I don’t want to say ‘dirt,’ but as much information as possible.”

That skill set has made Harkins a high-demand retainer in a number of important New York criminal cases. In the past few years, he’s not only joined the defense teams of high-profile public enemies such as Maxwell, but also those of a number of crooked or allegedly criminal cops who’ve run on the wrong side of their own laws. In 2014, for instance, Harkins worked for Dr. Emily Dearden, a former N.Y.P.D. psychiatrist who was accused of shooting her husband in the back of the head while he slept. Dearden and her defense eventually pleaded down her charges from 25 years in prison to 3 and a half.

Harkins also worked with attorney Andrew Weinstein in his 2013 defense of one of the midshipmen accused of sexual assault at the U.S. Naval Academy, and in his 2016 defense of a high-ranking New York City police chief accused of bribery and fraud. (The N.Y.P.D. official eventually plead guilty to a lesser charge in 2018, which The New York Times called a “slap on the wrist.”)

Judelson, the bail bondsman, says that defending clients who are accused of terrible crimes comes with the territory. “I don’t like a lot of the clients that I deal with, I don’t like a lot of the crimes that they’ve allegedly done, but we’re just doing our job,” Judelson says. “We’re not judge and jury. We’re just moving the criminal-justice system along.”

Harkins’s track record of shoe-leather and tree-shaking is a sharp contrast to the realities of the FTX case, which is built around the testimony of a cast of computer jockeys—a far cry from the pipe hitters of the Mob. But maybe that’s exactly why he’s decided to take the case—Bankman-Fried’s near-pathological blunders in speaking to the press are the opposite of how Harkins works. (He was polite but firm in telling me he would not comment for this story.)

The New York Times reports that the prosecutors’ case against Bankman-Fried will lean on the testimony of his former girlfriend and top lieutenant Caroline Ellison, who, among other things, kept notes on her computer entitled “Things Sam Is Freaking Out About.” There are still plenty of trees to shake, in other words, and Harkins is the man who will be shaking them.

Jack Crosbie is a New York City-based journalist