The gigolo is not an attractive man. Thin-lipped and angular, Helg Sgarbi appears more bookish than rakish, and his blue eyes seem to telegraph a constant message: vulnerability and need. When I enter the visiting room at Munich's Stadelheim prison, he is slouched behind a long wooden table, sandwiched between two other inmates. A little girl plays on the floor while two brothers argue in low tones. Dressed in blue prison jeans and a collared jersey, arms folded high, Sgarbi looks bored, accustomed as he is to the salons of Monte Carlo, the spa resorts of Austria, and the company of sad, doting rich women.

When he sees me approach, followed by a translator, he appears startled. Sgarbi is expecting his lawyer, not a complete stranger. Perhaps I am a hit man, sent by a cuckolded husband. A former Credit Suisse banker, the 44-year-old Sgarbi used to make his living preying on lonely women of means, seducing them, videotaping them having sex with him, and blackmailing them. That is, until the summer of 2007, when he took on three for-profit affairs simultaneously, including the one with his prize catch—Susanne Klatten, the married heiress to the BMW fortune and the richest woman in Germany, worth $12 billion—who became his downfall. Tabloids called him the "Swiss Gigolo," and he ranks as the most notorious con-man Lothario in the world today, a grifter accused of swindling a half-dozen women (though one eventually dropped the charges) out of more than $38 million in the course of his career.

I assure Sgarbi I am not here to hurt him, that I have met with his lawyer. He cuts me off: "You spoke to my lawyer about my case?" he says in English. "I did not give permission." In fact, Sgarbi's attorney offered to broker an interview—for a few hundred euros—and is looking to cut a deal for the film rights to Sgarbi's life story. You can see Sgarbi struggling to keep up with who is selling what to whom. "I am sorry you have come all this way," he says, sounding quite genteel, as he stands. "But there is nothing that I can tell you."

There is plenty Sgarbi could say but hasn't. In March, he averted what would surely have been a long and sensational trial by delivering a bombshell five-line confession on his first day in court. It conveniently saved him and the powerful Klatten, or "Lady BMW," as the press calls her, from having to air in public the lurid details of their affair—which included a videotaped sex romp at a Holiday Inn. Although prosecutors asked that Sgarbi serve nine years in prison for fraud and blackmail, the judges sentenced him to only six after he confessed. Sgarbi, who is fluent in six languages, got to keep his mouth shut—and his ill-gotten millions hidden.

But now comes a noisy sideshow that could threaten Sgarbi's fortune. This month, Italian prosecutors will put Sgarbi's alleged puppet-master, a 64-year-old former mechanic, on trial for "criminal association." Police say Ernano Barretta, an Italian religious-sect leader who claims to be a faith healer and allegedly has used female followers for sex, controlled Sgarbi, helping him target women, videotape them, and spend their money—conveniently enough, by buying resort properties in Egypt and splurging on Ferraris and Lamborghinis. What Barretta couldn't spend, Italian prosecutors say, he buried on his estate, near a 13th-century village close to the Adriatic coast.