Presidential candidate Scott Walker won a major legal victory Thursday when the Wisconsin Supreme Court ended a secret investigation into whether the Republican's gubernatorial campaign illegally coordinated with conservative groups during the 2012 recall election.
 
No one has been charged in the so-called John Doe probe, Wisconsin's version of a grand jury investigation in which information is tightly controlled. But questions about the investigation have dogged Walker for months.

Barring an appeal to the U.S. Supreme Court, the ruling makes Walker's campaign for the White House that much smoother as he courts voters in early primary states.

"Today's ruling confirmed no laws were broken, a ruling that was previously stated by both a state and federal judge," Walker spokeswoman AshLee Strong said. "It is time to move past this unwarranted investigation that has cost taxpayers hundreds of thousands of dollars."

The case centers on political activity conducted by the Wisconsin Club for Growth and other conservative organizations during the recall, which was spurred by Democrats' anger over Walker's law that effectively ended collective bargaining for most public workers.

The justices cited free speech, ruling that state election law is overbroad and vague in defining what amounts to "political purposes."

In the majority opinion, Justice Michael Gableman, part of the court's conservative majority, praised conservative groups for challenging the investigation, saying it was fortunate that prosecutors targeted "innocent citizens who had both the will and the means to fight the unlimited resources of an unjust prosecution."

Prosecutors alleged the groups and the campaign coordinated on issue advocacy, communications that do not expressly call for a candidate to be elected or defeated, and should have reported their spending and abided by fundraising limits. They denied any wrongdoing.