The recent acquittal of Jeronimo Yanez in Minnesota and the second deadlocked jury for Ray Tensing in Cincinnati illustrate how difficult it is for prosecutors to get convictions of police officers involved in on-duty fatal shootings. Police work is inherently dangerous. Officers are trained in use of force–that is, when they are justified in using it and how much they can use. The force they are permitted to use escalates with their reasonable perception of the threat against them. For example, they don’t have to see a gun in order to be justified in shooting someone; they need to perceive what they believe to be furtive movements toward a possible gun. In the case of Philando Castile, the victim in Minnesota who was shot last year after telling Officer Yanez that he had a gun (which he was licensed to…