Criminal justice experts note that, while the federal government and national research groups keep scads of data and statistics — on topics ranging from how many people were victims of unprovoked shark attacks (53 in 2013) to the number of hogs and pigs living on farms in the U.S. (upwards of 64,000,000 according to 2010 numbers) — there is no reliable national data on how many people are shot by police officers each year.

A report by the Washington Post says officials with the Justice Department keep no comprehensive database or record of police shootings, instead allowing the nation’s more than 17,000 law enforcement agencies to self-report officer-involved shootings as part of the FBI’s annual data on "justifiable homicides" by law enforcement.

That number – which only includes self-reported information from about 750 law enforcement agencies – hovers around 400 "justifiable homicides" by police officers each year. The DOJ's Bureau of Justice Statistics also tracks "arrest-related deaths." But the department stopped releasing those numbers after 2009, because, like the FBI data, they were widely regarded as unreliable.

Read more here.