Events which have cast doubt on the police

In light of recent events that have cast doubt on the police, here is a potential solution. The constitution stipulates that Congress can establish “tribunals inferior to the Supreme Court.” So let Congress establish special Federal civilian tribunals tasked with nothing more than investigating, charging and prosecuting police. This would prevent the police, or people who work closely with them, being responsible for handling misconduct by the police and ensure that such investigations have teeth. There would have to be a law that the tribunals could not be more than 50% staffed by ex police or people connected to the police.