In the spring and summer of 2008 — before the Great Recession — Tom Petters was pretty much a curiosity in the Twin Cities business community.

He’d made a few headlines with his investment in Fin­gerhut, the retail catalog business based in St. Cloud that provided jobs for folks in his hometown. He also owned and propped up then-struggling Sun Country Airlines and had acquired Polaroid with the hope of restoring cachet to an iconic American brand.

His employees found him charismatic. At the company’s lavish annual Christmas party, Petters would move from table to table, schmoozing. He’d kiss the cheek of every woman in the room and shake the hand of every man.

Only a few of his closest associates knew that Tom Petters was living a lie. The millions he spent to expand his corporate empire were “earned” by deception.

That would change on Sept. 24, 2008, when federal agents surrounded the Petters corporate campus in Minnetonka and conducted a daylong search for evidence of a massive fraud.

Now, nearly five years later, the criminal investigation that was spawned by the guilty conscience of whistleblower Deanna Coleman has basically come to a close. The conviction last week of hedge fund manager James Fry, who lost $100 million of his investors’ money doing business with Petters, resolved the last remaining case in the $3.65 billion Ponzi scheme that criminally snared 13 individuals overall.

“Nothing else is pending that is public,” Assistant U.S. Attorney Tim Rank said outside the St. Paul courtroom where Fry was convicted on all 12 counts Wednesday. But in between the arrest of Petters and the conviction of Fry lies one of the most compelling criminal investigations in state history.

“This was off the charts in terms of size and scope,” recalled Joe Dixon, the former assistant U.S. attorney who was in the center of the Petters case. Dixon’s comments to the Star Tribune are among the few public ones he’s made since his surgeon-like cross-examination of Petters that helped bring a 20-count conviction against the former Wayzata businessman.

The case went from zero to overdrive in a matter of days after prosecutors listened to Coleman’s story and began throwing all the agents and lawyers they could muster into the investigation.

“On Sept. 8, myself, two FBI agents and an IRS agent met with Deanna Coleman, who put in our lap incredible allegations of fraud that required an immediate response,” Dixon said. “After about an hour, we conferred and decided to send her back to Petters headquarters and start taping conversations. We knew we had to act right then and there.”

Coleman had confessed to prosecutors about a decadelong fraud in which Petters and his close circle of associates raised money from investors for the purported purchase of surplus consumer electronic goods to be sold to retailers such as Costco and Sam’s Club at a profit. But there were no electronic goods and no retail transactions. Money from new investors simply was used to pay off old investors.

With Coleman’s evidence in hand, prosecutors assembled a squad of 125 agents to search the property.

“This case is a reflection of the enormous power that federal prosecutors have,” said Ted Sampsell-Jones, a William Mitchell College of Law professor who followed the case from day one. “When they want to bring something down, they can do it.”

At the time of the raid and subsequent arrest of Petters, the allegations against his operation constituted the largest Ponzi scheme in U.S. history. But three months later the Petters case was dwarfed by the $65 billion Ponzi scheme of Bernard Madoff of New York and later the $7 billion Ponzi scheme of Texan Allen Stanford.

The fact that Petters was arrested in October of 2008 and was in court and on trial by November of 2009 is also a testament to the priority assigned to the case.

“That is pretty quick for a case of that size,” said Sampsell-Jones, who teaches criminal law. “Coleman made it easy. The feds knew what they were looking for. They had tons of evidence and documents for the jury. It was a layup for them.”

Dixon would dispute the “layup” notion but he does acknowledge that Coleman’s whistle-blowing helped speed things up.

“In a typical fraud case, after it implodes investors spend years poring through records. We would have prosecuted a number of individuals [in the Petters case] but it would have been less quickly and less efficiently,” Dixon said. “She gave us a good road map and good evidence.”

Today, Petters spends his days in the federal penitentiary in Leavenworth, Kan.

Five who helped run the scheme are also serving prison sentences ranging in length from five to 11 years. Sentences have yet to be imposed on five others, including Fry.

For Coleman, who served a sentence of 366 days and now lives in northern Minnesota, the notoriety of being a whistleblower seems to have taken a toll. “I just want it over with,” Coleman said plaintively near the end of her testimony in the Fry trial two weeks ago.