Law Enforcement Data

Philip Bump writes at The Washington Post:

It's not easy to figure out how many people have been killed by the police in the United States. The FBI compiles a wealth of information on crime and law enforcement each year as part of its Uniform Crime Reports system. But it only collects two points of data on people killed by law enforcement: The number of people killed by police in justifiable action, and the weapon used in the homicides. (Unjustified homicides are counted, too, of course: as crimes.)

What's more, as USA Today notes in its look at the data on Friday, only 750 of the nation's 17,000-plus law enforcement agencies contribute data to the FBI's justifiable homicide database. That's a huge caveat, particularly given that we can't ascertain how representative the pool of agencies might be. (We reached out the FBI for more information and didn't hear back.)

In 2012, the Bureau of Justice Statistics reported:

In September 2008, federal agencies employed approximately 120,000 full-time law enforcement officers who were authorized to make arrests and carry firearms in the United States. This was the equivalent of 40 officers per 100,000 residents. The number of federal officers in the United States increased by about 15,000, or 14%, between 2004 and 2008. Federal agencies also employed nearly 1,600 officers in the U.S. territories in 2008, primarily in Puerto Rico.
...

Excluding offices of inspectors general, 24 federal agencies employed 250 or more full-time personnel with arrest and firearm authority in the United States (table 1). These agencies employed 96% of all federal officers. The four largest agencies, two in the Department of Homeland Security (DHS) and two in the Department of Justice (DOJ), employed about two-thirds of all officers. Overall, DHS and DOJ agencies employed about 4 in 5 federal officers.