POPLAR BLUFF, Mo. -- A criminal investigation has begun into possible acts of illegal purchasing and bidding practices within the Poplar Bluff city manager's office.

The Butler County Sheriff's Department issued letters Friday notifying all members of the Poplar Bluff City Council.

The council fired city manager Heath Kaplan on May 12 after nine months on the job.

Other action taken by the council during the meeting has not been released, despite the 72-hour deadline set by state law to make public all closed session actions.

City officials have not said why the information is being withheld. Messages for interim city manager Mark Massingham were not returned.

The investigation is not intended to infer anyone's guilt, Sheriff Mark Dobbs said in letters to council members.

"As is in all investigations, there is the potential for criminal findings; however, there is also the potential to clear up ambiguous situations and exonerate certain individuals," he wrote.

Dobbs did not state which bids are under investigation.

He asked for full cooperation and transparency from the city.

The investigation could later include other agencies, such as the Missouri State Highway Patrol.

These decisions will come after it is determined what type of statutes may have been violated, Dobbs said.

The investigation was not begun at the request of any one individual, he said.

"It's more so out of observations of my own. It's not a whole lot different than watching a burglary in progress," he said. "If I see it occurring in my presence, I have an obligation to act."

This investigation will take time and likely require investigative subpoenas for documents and to conduct interviews, Dobbs said.