The FBI conducted a raid at the Detroit Public Library this morning.
The Detroit News reports agents arrived around 8 a.m. and left around 11 a.m.
The agents left carrying cardboard boxes and computer equipment, according to the News.
Library spokesman A.J. Funchess said agents presented search warrants when they arrived but didn't go into detail about the investigation.
"I don't know how many warrants," Funchess said. "They aren't really sharing a lot of information right now."
Agents spent much of their time in the offices of Tim Cromer, chief administrative officer. He has been the focus of several controversies over spending.
The focus of the FBI raid was unclear Tuesday, but library union leader Todd Kelly called it a "sad day."