Robert Bates (left), a Tulsa County, Okla., reserve deputy, leaves his arraignment Tuesday with his attorney. Bates fatally shot a suspect who was pinned down by officers, raising alarms about volunteer police officers who wear badges and carry guns. Sue Ogrocki/AP hide caption

itoggle caption Sue Ogrocki/AP

Rick Ector trains new gun owners at a range just outside of Detroit. He supports more African-Americans getting permits to carry concealed weapons. Martin Kaste/NPR hide caption

itoggle caption Martin Kaste/NPR

Detective Mark Williams (right) speaks with an officer in Richmond, Va. A decade ago, amid a surge in violent crime, Richmond police were identifying relatively few murder suspects. So the police department refocused its efforts to bring up its "clearance rate." Alex Matzke for NPR hide caption

itoggle caption Alex Matzke for NPR

Some colleges and police departments are starting to use software that scans social media to identify local threats, but most tips still come from members of the public. Ikon Images/Getty Images hide caption

itoggle caption Ikon Images/Getty Images