Reason has previously noted that for 2013, violent crime in the United States is down, killing of police officers (and violence directed toward police officers) is down, but homicides by police that were subsequently ruled justified were up. Law enforcement officers killed more than 400 people in 2013.

But that number is known to be incomplete. The FBI tracks justified homicides by police, but participation is voluntary. There is no actual national tracking of deaths at the hands of police unless they are to determined to be crimes and therefore show up in violent crime statistics. We don't have a real, credible number of how many people the police kill every year. So The Wall Street Journal attempted to compare numbers from law enforcement agencies with the numbers on the FBI's reports between the years 2007 and 2012. They found more than 500 deaths at the hands of law enforcement agencies unaccounted for in the FBI's reports. They conclude "it's nearly impossible to determine how many people are killed by the police each year":

The reports to the FBI are part of its uniform crime reporting program. Local law-enforcement agencies aren't required to participate. Some localities turn over crime statistics, but not detailed records describing each homicide, which is the only way particular kinds of killings, including those by police, are tracked by the FBI. The records, which are supposed to document every homicide, are sent from local police agencies to state reporting bodies, which forward the data to the FBI. The Journal's analysis identified several holes in the FBI data. Justifiable police homicides from 35 of the 105 large agencies contacted by the Journal didn't appear in the FBI records at all. Some agencies said they didn't view justifiable homicides by law-enforcement officers as events that should be reported. The Fairfax County Police Department in Virginia, for example, said it didn't consider such cases to be an "actual offense," and thus doesn't report them to the FBI.

The State of New York does not participate in the reporting program, according to the Journal, and therefore 68 homicides by New York City Police Department officers between the years 2007 to 2012 are not even in the FBI's count. It also means that Eric Garner's choking death at the hands of officers from the NYPD will not show up in the numbers next year when the FBI releases its statistics for 2014.

Read the Wall Street Journal analysis here.

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