MADISON, Wis. (AP) — Prosecutors believe Wisconsin Gov. Scott Walker, a potential 2016 Republican candidate for president, was at the center of a nationwide “criminal scheme” to illegally coordinate fundraising with outside conservative groups, according to previously secret court documents released Thursday.

The documents were filed as part of an ongoing lawsuit challenging the probe by the conservative group Wisconsin Club for Growth. They were ordered publicly released Thursday by a federal appeals court judge after prosecutors and the Wisconsin Club for Growth did not object.

AP Photo/Jeffrey Phelps, File

One of the filings from prosecutors outlines previously unknown details about the investigation that began in 2012 as Walker was facing a recall election.

“The scope of the criminal scheme under investigation is expansive,” lead investigator Francis Schmitz wrote in the Dec. 9 court filing. “It includes criminal violations of multiple elections laws” including filing false campaign reports, he wrote.

Prosecutors said Walker, his chief of staff Keith Gilkes and top adviser R.J. Johnson were discussing illegal coordination with a number of national groups and prominent figures, including GOP strategist Karl Rove.

Walker’s campaign spokeswoman, Gilkes and Johnson did not immediately return messages seeking comment. While he eyes a run for president, Walker is seeking re-election this year against likely Democratic nominee Mary Burke.

Walker rose to fame shortly after taking office in 2011, passing a bill that effectively ended collective bargaining for most public workers. The uproar over that law led to Walker’s recall election in 2012, which he won, making him the first governor in U.S. history to ever defeat a recall.

The investigation, which began in secret in 2012, focuses on Walker’s campaign and other conservative groups. U.S. District Judge Frank Easterbrook on Thursday ordered the release of more than 250 pages of court documents, many pages of which had previously been secret.