Metropolitan Division officers finish another "rollback" operation. They searched the apartment of a paroled armed robber and gang member. These rollbacks are a cornerstone of the Metro Division's strategy of tracking people who may re-offend, and suppressing crime before it happens. Martin Kaste/NPR hide caption

itoggle caption Martin Kaste/NPR

Taser International is now selling police departments the technology to store videos from body cameras. Patrick T. Fallon/Bloomberg via Getty Images hide caption

itoggle caption Patrick T. Fallon/Bloomberg via Getty Images

License plate scanners have helped police locate stolen vehicles and have even assisted in murder investigations. But with their ability to track a person's every move, skeptics worry about privacy. Pablo Martinez Monsivais/AP hide caption

itoggle caption Pablo Martinez Monsivais/AP

Officers stand watch at the intersection of West North Avenue and Pennsylvania Avenue as protesters walk for Freddie Gray in Baltimore in April. Gray died from spinal injuries about a week after he was arrested and transported in a police van. Jabin Botsford/The Washington Post/Getty Images hide caption

itoggle caption Jabin Botsford/The Washington Post/Getty Images

A Maryland state trooper stands guard near a CVS pharmacy that was destroyed during rioting in Baltimore this week. Andrew Burton/Getty Images hide caption

itoggle caption Andrew Burton/Getty Images

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