A federal appeals court threw out the arson conviction of a man who calls himself "Dr. Chaos," (search) saying he should have been allowed to withdraw his guilty plea before being sentenced to 21 years in prison.

Joseph Konopka (search) pleaded guilty in 2002 to six federal crimes, including arson (search), but tried to back out of the plea before his sentencing a year ago. He argued that a federal statute that would add 10 years to his sentence for using fire while committing the crimes shouldn't apply when the crime is arson.

U.S. District Judge Lynn Adelman of Milwaukee refused him, but a three-judge panel of the 7th Circuit Court of Appeals in Chicago upheld the appeal.

"Why would Congress want the use of fire to enhance the punishment for using fire?" Judge Richard Posner wrote in a five-page opinion Tuesday.

Konopka, 28, is serving his sentence concurrently with a 13-year-prison term in Illinois for hiding bottles of cyanide in tunnels of Chicago's subway system. The appeals court decision does not affect his other convictions.

Francie Wendelborn, a spokeswoman for the U.S. attorney's office in Milwaukee, said prosecutors will try to work out a compromise sentence with Konopka, but he would be tried if a deal can't be reached. Konopka's attorney, Bridget Boyle, said she would study all the options.

Prosecutors said Konopka was the self-appointed leader of a loose affiliation called "The Realm of Chaos," which recruited youths to engage in property damage.

Konopka was sentenced for conspiring to knock out power lines, burn buildings and damage computers in Wisconsin. Authorities said more than 50 acts in various Wisconsin counties affected more than 30,000 power customers and caused more than $800,000 in damages.