By Ian Simpson
WASHINGTON (Reuters) - A long-running investigation into the 2010 election campaign of former District of Columbia Mayor Vincent Gray has concluded, and no charges will be filed against him, U.S. prosecutors said on Wednesday.
The probe found evidence of more than $3.3 million in illegal contributions in various campaigns between 2006 and 2011, including the 2008 presidential campaign, the U.S. Attorney's Office said in a statement.
"No additional charges are expected to be filed in the investigation related to the federal and local political campaigns," it said.
Although the statement did not mention Gray, a Democrat, by name, he had been a focus of speculation about possible charges involving his 2010 election. Gray, 73, turned down a plea deal in November 2014 that called for him to plead guilty to a felony.
Gray's attorney, Robert Bennett, was not immediately available to comment.
A dozen people have pleaded guilty to charges in the investigation, which began in 2011. They include seven who pleaded guilty to offenses linked to the 2010 election won by Gray.
Gray, who presided over a booming economy and rising population in the U.S. capital, lost the Democratic primary to council member Muriel Bowser in April 2014 as the investigation became an election issue. She went on to win the general election in November.
The most damning claims against Gray aired in court files and hearings focused on his alleged knowledge of a $653,000 "shadow campaign" on his behalf funded by businessman Jeffrey Thompson and executed by close associates Jeanne Clarke Harris and Vernon Hawkins.
Gray was also dogged by revelations that a rival candidate, Sulaimon Brown, had been paid secretly by Gray associates to boost Gray's chances by staying in the race and verbally attacking Democratic incumbent Adrian Fenty.
Prosecutors have asked judges to set sentencing dates for the seven who have pleaded guilty, the statement said.