Federal judges Thursday ruled that former state purchasing supervisor Georgia L. Thompson was wrongly convicted of making sure a state travel contract went to a firm linked to Gov. Jim Doyle's re-election campaign and freed her from an Illinois prison.

The three-judge panel in Chicago acted with unusual speed, ruling after oral arguments by Thompson's attorney and the U.S. attorney's office.

During 26 minutes of oral arguments, all three judges assailed the government's case, with Judge Diane Wood saying at one point that "the evidence is beyond thin."

During a news conference later Thursday, Doyle, a former state attorney general, said the three judges did an "extraordinary thing" by entering an order finding Thompson innocent and ordering her immediate release.

Decisions at that level of the federal judicial system usually take weeks or months after oral arguments.

To charge her, Mr. Biskupic had to look past a mountain of evidence of innocence. Ms. Thompson was not a Doyle partisan. She was a civil servant, hired by a Republican governor, with no identifiable interest in politics. She was only one member of a seven-person committee that evaluated the bidders. She was not even aware of the Adelman campaign contributions. She also had a good explanation for her choice: of the 10 travel agencies that competed, Adelman submitted the lowest-cost bid.

While Ms. Thompson did her job conscientiously, that is less clear of Mr. Biskupic. The decision to award the contract — the supposed crime — occurred in Madison, in the jurisdiction of Wisconsin’s other United States attorney. But for reasons that are hard to understand, the Milwaukee-based Mr. Biskupic swept in and took the case.

While he was investigating, in the fall of 2005, Mr. Biskupic informed the media. Justice Department guidelines say federal prosecutors can publicly discuss investigations before an indictment only under extraordinary circumstances. This case hardly met that test.

The prosecution proceeded on a schedule that worked out perfectly for the Republican candidate for governor. Mr. Biskupic announced Ms. Thompson’s indictment in January 2006. She went to trial that summer, and was sentenced in late September, weeks before the election.

Most of the eight dismissed prosecutors came from swing states, and Democrats suspect they may have been purged to make room for prosecutors who would help Republicans win close elections. If so, it might also mean that United States attorneys in all swing states were under unusual pressure.

Wisconsin may be the closest swing state of all. President Bush lost it in 2004 by about 12,000 votes, and in 2000, by about half that. According to some Wisconsin politicians, Karl Rove said that their state was his highest priority among governor’s races in 2006, because he believed a Republican governor could help the party win Wisconsin in the 2008 presidential election.