Police officers point their weapons at demonstrators in Ferguson, Missouri, August 18, 2014. (Credit: Reuters/Joshua Lott)

The shooting of teenager Michael Brown has focused the nation (again) on the dangers faced by young, unarmed black men walking the streets of America. The sight of paramilitary police with guns pointed at peaceful protesters in a suburban town in the Midwest also got our attention. And as we wait for the legal system to determine if officer Darren Wilson will be held liable for the shooting, new questions are rising to the surface about the issue of officer-involved shootings in general. How often does this happen? How are these issues normally handled by prosecutors and the courts? And surprisingly, there is almost no way of knowing how often American citizens are killed at the hands of the authorities.

Most reporting in the last couple of weeks has cited the figure of 400 people killed in incidents of ‘justifiable homicide” by police officers each year […]