It is important that those responsible for the police force can not just simply wash themselves clean of the problem by firing the lowest level employees. I do not disagree that individuals need to be held responsible for their own actions, through most blames should lie on those who hold power to create real change in the organization. As an generalization, a good model is one where blames travels upward and praise travel downward.
Just voting differently is naturally not the only way a government can be held responsible. Political assigned jobs is a job description based on trust, and there should be mechanism to remove individuals who do not fulfill that trust. Governments should also be liable to their citizens, so when injustice occurs people should have the option to demand compensation from the government. This in turn put pressure on politicians to avoid injustice caused by the police.
A police force that protects citizens rights should be viewed as an asset to local government, and the opposite should be a harsh liability that local governments can feel.