WARREN, Mich. -

Warren City Hall 2 Local 4 was first to learn of the federal investigation at Warren City Hall at the beginning of August.

Sources at City Hall have confirmed federal agents went there Aug. 8 armed with subpoenas and headed straight to Mayor Jim Fouts' office.

Rumblings about the nature of the subpoenas continued but initial calls to the city claimed no federal subpoenas had been served.

To get to the bottom of this, Local 4 filed a FOIA request at the end of August asking for any subpoenas, search warrants and other documents filed by the U.S. Attorney's Office or FBI.

The city of Warren returned that FOIA at the end of five days. They said they had every right to extending their time by 10 more days to consider their request.

So what are the federal investigators looking for?

Sources close to the investigation tell Local 4 they are looking at several issues in what was described to Local 4 as multiple federal subpoenas served on the city investigating possible public corruption.

City of Warren DPW The city of Warren had 3,600 tons of salt go missing from its public works salt dome this past January. It was about $175,000 worth of salt.

There also were questions about expensive tires for the city's fleet of garbage trucks and questions raised about Warren's contract with the Detroit Incinerator.

After initially telling Local 4 he had no comment, Fouts sent out a statement to all media which in part reads, "We have and will continue to cooperate with the Grand Jury by supplying all records that were requested. I am proud of my record of honesty, transparency and forthrightness during my 31 years in city government."

Sources close to the investigation confirm the federal agents are interested in one of Fouts' top appointees, Gust Ghanam. Ghanam is Warren's sanitation director and the FBI is looking for information on Ghanam and his contracts for garbage trucks as well as his dealing with the city of Detroit's incinerator.

The city tells us it will consider turning over documentation on or after Sept. 24.

Read: Mayor Jim Fouts' full statement

Warren City Hall 1