Our department conducts an IA investigation. The officer is assigned to inside, desk duty until the investigation is complete. It's a small department, so it doesn't take more than a few days. As in all use of deadly force, the incident is brought before the Grand Jury. They must determine that no crime was committed before the officer is ultimately cleared. If they determine that the officer was wrong. He is charged with the associated crime (assault first, murder, manslaughter, etc.). The officer would be arrested like any other criminal.