Joe Dixon III, the laser-focused former federal prosecutor who helped send Tom Petters and a handful of other high-profile white collar criminals to prison, is moving to the defense side of the bar with the Minneapolis law firm of Fredrikson & Byron.

Starting Monday, Dixon will be co-chairman of Fredrikson's white-collar practice, which includes 12 attorneys and represents both individuals and corporate clients in criminal investigations and regulatory disputes.

Dixon's move comes 3 ½ years after he left the U.S. attorney's office in Minnesota as deputy criminal chief for a high-level position in the legal department of Minnetonka-based UnitedHealth Group Inc., the nation's largest health insurer.

For Dixon, the lure of the courtroom was too strong to resist.

"What I enjoy most is representing clients who are in heated disputes," Dixon said in an interview Wednesday. "Presenting a case to a jury is the apex of what the judicial system is about."

Ironically, the prosecutor best known for leading the charge against Petters and his $3.65 billion Ponzi scheme is joining a firm that represented Petters and his businesses for more than 10 years.

"It's no secret that I prosecuted Mr. Petters, and it's no secret that Fredrikson represented Mr. Petters prior to his criminal allegations … but I have no concerns about Fredrikson," Dixon said. "It is an outstanding firm. If I had any concerns, I wouldn't have joined it."

In 2012, the firm paid $13.5 million to the Petters bankruptcy estate to settle a lawsuit filed by the bankruptcy trustee to recover attorney's fees paid by Petters and his companies. The firm admitted no wrongdoing.

Dixon said he chose Fredrikson for his practice in part because of its nearly 20-year history in white-collar defense work and its growth potential with offices in North Dakota, Iowa, Mexico and China.

"This is a firm that knows who they are and where they are going," he said.

Dixon's co-chair in the white-collar group is Dulce Foster, another veteran.

Fredrikson President John Koneck said the firm believed Dixon's "unique blend of public prosecutorial and private legal and business experience" would enhance its group of trial lawyers.

Dixon is the latest on a list of former federal prosecutors in Minnesota who took their Department of Justice experience into private practice.

Current U.S. Attorney Andrew Luger has spent some of his career as a defense attorney. So have former U.S. Attorney B. Todd Jones and assistant prosecutors Jon Hopeman, Doug Kelley, Earl Gray and Dan Scott.

But Hank Shea, a former assistant U.S. attorney who now teaches at the University of St. Thomas School of Law School, said Dixon's route to the defense table is different because of his stop at UnitedHealth, where he was responsible for internal investigations into matters such as the False Claims Act and Foreign Corrupt Practices Act. He also responded to congressional inquiries for the company and worked on implementation of elements of the Affordable Health Care Act.

"He was trying to get ahead of issues and problems before they became more serious," Shea said. "Joe, at his heart, wants to make the community better. By going to Fredrikson, he has a greater opportunity to do that."

Dixon's résumé as a criminal prosecutor includes supervision of the conviction of automobile mogul Denny Hecker; the sentencing of hedge fund manager Trevor Cook, who went to prison for 25 years for the $165 million fraud he engineered; and the prosecution of former state legislator Loren Jennings for abuse of his office.

But to those in criminal legal circles, Dixon is perhaps best known for the Petters case and his surgical cross-examination of the former Wayzata businessman who was convicted on fraud charges in 2009 and sentenced to 50 years in prison.

"In the case of Mr. Petters, who was a tremendous salesman, it was the first opportunity to ask him tough questions," Dixon said. "It was a series of difficult moments where Mr. Petters was forced to reveal his true colors."