About 4,500 more ballots than registered voters were cast in the election last November in Milwaukee, investigators said Tuesday.

Also, more than 200 felons voted improperly in Milwaukee, and more than 100 instances of suspected double-voting were found.

No charges have been filed. Investigators found no widespread conspiracy, just isolated incidents, U.S. Attorney Steven Biskupic said.

"I don't think there's an election in this municipality or this state that would have been decided differently even with those numbers," said Mayor Tom Barrett, a Democrat.

Democrat John Kerry (search) received more than 71 percent of the 277,000 ballots cast in Milwaukee in the presidential race, and he took the state of Wisconsin by about 11,000 votes.

The investigation was launched by local and federal authorities after the Milwaukee Journal Sentinel found, among other things, that more than 1,200 people voted from invalid addresses. The head of the city's election commission has since resigned.

Wisconsin allows same-day registration, and those who are already registered can simply show up at the polls without ID.