There should be a federal law that requires any police-related deaths to be investigated by an independent, outside agency in order to protect citizens' lives and safety and to protect police, in the case of being wrongly accused.
Teachers, restaurant-owners, construction builders, and doctors are all held to standards and are routinely checked by outside agencies in order to ensure quality and to protect people's safety and health. Police, too, should have an agency to protect both them and the people that they serve.