The liberal Center for Media and Democracy has dug up a financial link between conservative interest groups and the federal judge who dramatically shut down a state-level investigation into Wisconsin Gov. Scott Walker’s (R) 2012 recall election.

Financial disclosure forms examined by the center show that U.S. District Judge Rudolph Randa has been a regular attendee at “judicial junkets” organized by George Mason University and financed by groups including the Charles G. Koch Charitable Foundation, the Lynde and Harry Bradley Foundation, and the U.S. Chamber of Commerce. Randa attended the all-expenses-paid judicial seminars in 2006, 2008, 2010, and 2012. The seminars are privately-funded, and the backers also include corporations like BP, Exxon Mobil, and Dow Chemical.

According to the Center for Media and Democracy, the seminars have a “decidedly pro-corporate bent,” but it is not known whether campaign finance issues were discussed as the seminars Randa attended.

Earlier this month, Randa issued a sharply-worded ruling ordering Wisconsin prosecutors to halt a secret “John Doe” investigation targeting alleged illegal campaign coordination between Walker’s campaign and outside conservative groups. Campaign finance watchers took notice of Randa’s language. One federal election commissioner told TPM that if Randa’s ruling were to be “carried out to its full meaning, there would be very few campaign [finance] laws that would continue to be able to be enforced.”

The Charles G. Koch Charitable Foundation has given millions of dollars to George Mason over the years, and in 2012 it contributed $51,000 to the university’s “Law and Economics Center,” according to the Center for Media and Democracy. The Bradley Foundation, meanwhile, has contributed tens of thousands, including $40,000 in 2010 “to support educational programs for judges conducted by the Law and Economics Center.” The Center for Media and Democracy reports that Michael Grebe, the president and CEO of the Bradley Foundation, chaired Walker’s 2010 and 2010 gubernatorial campaigns.