All complaints made by civilians are initially processed by the independent agency Civilian Office of Police Accountability, which then assigns them to the proper agency.
Currently, COPA investigates certain types of serious complaints against Chicago Police officers, including excessive force, domestic violence, and improper search and seizure. COPA also investigates all officer-involved shootings. All other complaints are investigated by CPD officers, typically police supervisors or officers assigned to the Bureau of Internal Affairs.
The implicated officers will be notified of the complaint. The investigators will collect evidence, conduct interviews, and prepare their findings. A complaint can either be sustained or unsustained. If the complaint is sustained, the agency will recommend the appropriate discipline. There is then a legal review process that allows for appeal.
The Chicago Police Board is the agency that makes the final decision about whether to discipline an officer.
On COPA’s website, there is a detailed explanation of the Investigative Process.