A federal investigation into the police killing of an unarmed, black 18-year-old in Ferguson, Missouri, lays bare what officials contend are racist, profit-driven law enforcement practices in the small St. Louis suburb.

The Department of Justice cleared Officer Darren Wilson of federal civil rights charges in the August death of Michael Brown. But it also called for sweeping changes in a city where officers trade racist emails, issue tickets mostly to black drivers that generate millions of dollars in revenue, and routinely use what investigators called excessive force on people stopped for minor or nonexistent offenses.

Ferguson Mayor James Knowles III said Wednesday that steps are already being taken to correct problems.

Separate federal investigations into the shooting and the police department began soon after Brown was killed.