Officer-involved shootings have dominated the headlines across the country.
Locally in Los Angeles County, KPCC's investigation found that one in four people shot by officers between 2010 to 2014 were unarmed. Of all the people that officers killed, black people were killed at triple the rate of whites and Latinos.
Gathering this data was not easy to come by. KPCC did it by sourcing this information from the L.A. District Attorney's office. Compiling a database on the national level is a much more difficult task.
Frank Zimring, professor of law at UC Berkeley and director of the criminal justice research program at the Earl Warren Legal Institute, recently published his own report on the number of killings both by and of police officers dating back to 1976.
"All of the official statistical tallies, including the ones we used in the article that's now out, actually were only capturing about half of the killings that took place," he says. "All of them are supposed to be comprehensive. All of them are off by half and for different reasons."
The Uniform Crime Report gathered by the FBI does not gather information from every city or state, for example, nor does it check the validity of what's contained in each report.
"They are the police departments' word for what happened. Nobody challenges them," he says.
The Bureau of Justice Statistics found that its report only found that a killing took place in half of incidents.
Meanwhile Vital Statistics data is compiled by county health departments and records every death in the U.S. However, departments do not assess the details of how a shooting death happened, only the cause of death.
Zimring argues that there is no uniform and robust source of national information because officer-involved shootings were traditionally seen as a local problem.
"People might simply talk about what happened when Officer Smith killed citizen Jones. We don't aggregate and we don't see this as a national problem," he says. "If the killing of civilians becomes a priority concern at the federal level of government in the United States, there could be tremendous progress in cutting the death toll."