A former Democratic Party county chairman in northern Indiana has been charged with leading a scheme to forge signatures on petitions to place Barack Obama and Hillary Clinton on the state's 2008 presidential primary ballot.

The St. Joseph County prosecutor's office filed felony conspiracy to commit forgery and other charges against 63-year-old Butch Morgan on Monday. Three former workers in the county voter registration office also face forgery and other charges.

Prosecutors contend in court documents that Morgan directed the workers to forge voter names and signatures onto Obama and Clinton petitions from valid petitions for Democratic gubernatorial hopeful Jim Schellinger. A state police detective found nine petitions submitted for Obama with forged entries and 13 petitions for Clinton with forgeries, according to an affidavit filed with the court.

Morgan denied any wrongdoing when he resigned in October following 16 years as county chairman after the South Bend Tribune and the Howey Politics Indiana newsletter reported they had found hundreds of questionable signatures on the Obama and Clinton petitions.

A phone message from The Associated Press on Tuesday seeking comment from Morgan's attorney, Mike Tuszynski, wasn't immediately returned.

The court documents say another voter registration office employee told investigators that Morgan told the workers to forge the petition signatures. That worker, who wasn't charged, showed investigators Obama petitions that he had faked and told police he saw one of the defendants forging names on Clinton petitions.

County Republican chairwoman Deb Fleming told the Tribune that all of those charged had let the citizens down. She said the Democrats, who have long dominated South Bend politics, have "a culture of corruption."

"I'm sure there are other things. They've just never gotten caught," Fleming said. "Because they've been in control of St. Joseph County for so long, they felt they could get away with it."

State Sen. John Broden, the county's current Democratic chairman, said the local party has cooperated fully with the investigation and that all those charged have been removed from the voter registration office.

"We remain committed to the integrity of the electoral process and will take every step necessary to keep the trust of local voters," Broden said.

The most serious of the criminal charges against Morgan and the workers carries a maximum possible sentence of eight years in prison.

Indiana law requires candidates for president, senator and governor to submit ballot petitions signed by at least 500 registered voters in each of the state's congressional districts to qualify for the statewide primary ballot. Clinton narrowly won the 2008 Indiana primary, but Obama won many delegates in his successful drive for the nomination. No such petition signatures are required for major parties to put their nominees on the general election ballot.

Names forged on the presidential petitions included former Gov. Joe Kernan and St. Joseph County Prosecutor Mike Dvorak.

The prosecutor's office said Tuesday that Dvorak was stepping aside in the case because he was a potential witness and that Stanley Levco, the former prosecutor in southern Indiana's Vanderburgh County, had been appointed as special prosecutor.

Jeff Kimmell, an attorney for charged registration worker Dustin Blythe, agreed with the appointment of an outside prosecutor and said that his client "remains confident he will be acquitted of all charges."