“Dude, Frankie Sparaco is in the hole,” Mean Gene, a fellow prisoner at FCI Loretto in Pennsylvania, told me on the move.

Why on earth would this popular mobster get thrown into single-cell segregation? I wondered. “That white boy from New York, Roger, punched him in the face and called him a rat,” Mean Gene explained. But I wasn’t buying it. I’d done time with Sparaco at several joints, and he was known as a solid convict. He also was nearing the end of his two decades in federal prison, getting ready to return home. A vicious dude and then some, but Sparaco was different from most mobsters I knew in jail.

“[He] was a very dangerous man back in his days on the street with the Colombos,” says Scott Burnstein, author of Mafia Prince: Inside America’s Most Violent Crime Family and the Bloody Fall of La Cosa Nostra. Sparaco was acting boss Alphonse “Allie Boy” Persico’s best friend and did a lot of his bidding. This included killing a guy who had been sleeping with Allie Boy’s wife, Burnstein says. “Guys were very afraid of him. When people saw him coming, they knew he was for real, who he spoke for and how much terror he could bring.”

Not only did he officially join Team USA against his former cohorts, but it also came out that he had been cooperating since the Colombo war.

Known as “Frankie Blue Eyes,” Sparaco was a top capo for imprisoned Colombo Don Carmine “the Snake” Persico. During the Colombo war that left a trail of dead mobsters on Brooklyn’s streets in the early 1990s, Sparaco was a shooter for the Persico faction, a group loyal to Carmine who was fighting off Victor “Little Vic” Orena’s leadership challenge. Sparaco was so close to the Persicos that Orena made plans to eliminate him first, according to Mafioso blogger Kenny Gallo. But he couldn’t get close to the elusive, savvy gangster who started killing those on Orena’s side.

The Persico faction, says Larry McShane, author of Chin: The Life and Crimes of Mafia Boss Vincent Gigante, was led by Greg “the Grim Reaper” Scarpa — “one of the FBI’s most valuable rats.” They had been fighting for control of the family, and “the Orena team, to this day, insists that the FBI backed the Persico faction in an effort to keep Scarpa in place and install him as boss,” says McShane. This basically gave “the feds a seat on the commission,” he adds, referring to the ruling commission in New York composed of five Mafia families.

Arrested in 1993, Sparaco pleaded guilty to five murders and was sentenced to 24 years in federal prison. But being in the big house didn’t stop him from making moves. Through an associate, Sparaco hooked up with John LeBoutillier, a Harvard grad, former Republican congressman and an heir to the Vanderbilt and Whitney fortunes. Sparaco proceeded to scam LeBoutillier for more than $800,000 from prison using an elaborate scheme that played on LeBoutillier’s belief that American prisoners of war from the Vietnam War were still being held captive in Russia and Southeast Asia.

McShane refers to the scam as “kind of genius.” Sparaco, he says, claimed he had contacts with jailed Russian gangsters who confided that there were as many as 75 American POWs from the Vietnam War era still imprisoned in Belarus. “It was all bogus, but LeBoutillier bit hard,” McShane adds. The former congressman visited Sparaco in prison, sending him money to supposedly pay the foreign gangsters for their info while advocating on Sparaco’s behalf to prison officials. “If I was scammed, I feel betrayed,” LeBoutillier would tell the Daily News.

But Sparaco saved his grandest feat for last. Threatened with new murder charges right before he was set to be released, Blue Eyes turned on his boss, Allie Boy, and spilled the beans. Not only did he officially join Team USA against his former cohorts, but it also came out that he had been cooperating since the Colombo war. He was a New York Whitey Bulger — in deep with the feds and getting paid since the 1980s, according to the New York Post.

Although it was Scarpa who earned a hefty share of media attention for carrying out murders while working simultaneously as a paid FBI informant, his playing both sides wasn’t unique. “He wasn’t the first, nor the last, gangster to do so,” says Christian Cipollini, author of Lucky Luciano: Mysterious Tales of a Gangland Legend. And revelations soon surfaced, making it clear that Sparaco, while cooperating with police in 2009, committed murder, and “two of the victims weren’t even Mafia or underworld figures at all,” Cipollini adds.

To spare himself more time, Sparaco gave info that led to Allie Boy’s conviction for the 1999 murder of “Wild Bill” Cutolo. But the feds acknowledged that they had been duped by Sparaco in the past, noting that Sparaco and Scarpa had lied and misrepresented their criminal culpability in the Colombo war, pointing fingers at others while pocketing government checks as they whacked rivals.

“Of course, the bureau denies agents had any knowledge of this,” Cipollini says. “But the feds knew all about it.”

*Squirreled away in the witness protection program, Sparaco wasn’t available for comment.