[throwaway290]

As non American it looks to me like this: you can't decide to arrest police chief for doing something but you can investigate it. He obstructed investigating, he gets a charge. Investigation ends, maybe other charges.

I guess it can be tricky to prosecute local police because it has to be interference from outside and people don't like that?

[qingcharles]

It's just super hard to prosecute police, because who do you report the misconduct to? If you go to the officer's police dept, they laugh at you. If you go to the local prosecutor -- well, they need the police to give them cases and evidence -- they laugh at you. If you try to go to the Sheriff, they laugh at you. If you go to the State Police or the FBI they tell you they don't have the resources and you need to go the police dept or prosecutor.

It's an unwinnable game. The only way to get traction is with media coverage.