Citing "deep mistrust" between residence and police, Attorney General Eric Holder announced the details of the DOJ's investigation Thursday.
He said the federal inquiry -- separate from one specifically examining the Aug. 9 shooting of Brown, 18, by Officer Darren Wilson -- will examine patterns of stops, arrests and use of force, as well as officer training.
"People consistently expressed concerns stemming from specific alleged incidents, from general policing practices, and from the lack of diversity on Ferguson's police force," Holder said Thursday. The investigation would probe whether the Ferguson police were "engaged in a pattern or practice of violations of the U.S. Constitution or federal law."
Just four of Ferguson's 54 officers are black, while the city population is more than two-thirds black. State statistics find that in St. Louis County, which includes Ferguson, officers are more likely to pull over blacks than whites, and are more likely to arrest black people in those traffic stops.
The DOJ reviewed police records before deciding whether to open the investigation. In the past five years, the Civil Rights Division at a the DOJ has opened more than 20 similar investigations and entered into more than 14 agreements to "reform law enforcement practices with agencies large and small."
Read the DOJ's full release here.