They don't always do, our city has done their own internal investigations before and not came to the same conclusion in their findings. High profile cases, attorneys of clients can file with the state for investigation. Police departments themselves, when there is an officer involved incident, can't investigate themselves, those cases are handed off to other police agencies. You can say it's one and the same, most cases that might be true, but it's not always 100% conclusive to that fact.