A longtime assistant U.S. attorney who played a significant role in the prosecution of some of Minnesota's largest fraud cases has left his government job to join Minnetonka-based UnitedHealth Group, Inc.

Joe Dixon, who spent 11 years at the U.S. Attorney's office in Minneapolis, left his position on Friday, according to spokeswoman Jeanne Cooney. He left the job to become deputy general counsel for government and internal investigation at UnitedHealth Group, she said.

UnitedHealth Group spokesman Tyler Mason confirmed via e-mail on Tuesday that Dixon officially started his new position on Monday, although he didn't specify what Dixon's new role will entail.

“Joe is joining a team of professionals who are focused on innovative ways to make the health care system work better for everyone,” Mason wrote.

In his former government role, Dixon worked primarily in the field of white-collar crime, most recently leading the white-collar division of the U.S. Attorney's office's criminal division. That role will be taken over by Tim Rank, who has worked at the U.S. Attorney's office for several years and has been recognized for his work on cyber crime prosecution, Cooney said, adding that Rank also worked on the Tom Petters case.

Dixon played key roles in the prosecution of Petters and the co-conspirators involved in the $3.65 billion Ponzi scheme that spanned a decade. He was also instrumental in other high-profile criminal cases, including the prosecutions of hedge fund manager Trevor Cook and former auto mogul Denny Hecker.

UnitedHealth Group is Minnesota's largest company based on its 2010 revenue, which totaled $94.1 billion. According to a report by the Star Tribune, the company has been realigning its legal team in recent months as it continues to expand its Optum health services division.