It took 6 months for a grand jury to exonerate another Wichita officer. http://www.texomashomepage.com/news/local-news/wichita-falls... The appeals etc took years after that. My point is, you don't let the cops make the determination about whether a cop is guilty. There are whole other layers of accountability.

Edit: and yeah I agree cops don't get convicted often enough. Either way a real investigation is going to take time.