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

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

Maria Hamilton (left) marches in Milwaukee with her sons on April 30 in remembrance of her son Dontre, who was shot and killed by a now-former police officer in a park last year. Hamilton founded Mothers for Justice United, which planned a march on Washington on Saturday to protest police violence. Carrie Antlfinger/AP hide caption

itoggle caption Carrie Antlfinger/AP

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

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Cellphones were used to record a 2012 confrontation between protesters and police in Springfield, Ill. Seth Perlman/AP hide caption

itoggle caption Seth Perlman/AP

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

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A crib sheet created to aid police-student interactions might be the first of its kind. The sheet was created by Akron, Ohio, high school students with help from the city's police department. M.L. Schultze /WKSU hide caption

itoggle caption M.L. Schultze /WKSU

Yonkers community activist Hector Santiago demonstrates the "stop-and-shake" with Lt. Pat McCormack of the Yonkers Police Department. The idea, Santiago says, is to get people to introduce themselves to cops on the street. Courtesy of Hector Santiago hide caption

itoggle caption Courtesy of Hector Santiago

Attorney Scott Rynecki and Kimberly Ballinger, the domestic partner of Akai Gurley, filed a lawsuit seeking $50 million against the city, the NYPD and officers Peter Liang and Shaun Landau. Bebeto Matthews/AP hide caption

itoggle caption Bebeto Matthews/AP

The Akron Police Department training class works out at Kent State Basic Police Officer Training Academy. Donald Clayton is the only African-American in the class of 20. M.L. Schultze/WKSU hide caption

itoggle caption M.L. Schultze/WKSU

New York Police Department Commissioner William Bratton attends a press conference after witnessing police being retrained under new guidelines at the Police Academy on Dec. 4. Andrew Burton/Getty Images hide caption

itoggle caption Andrew Burton/Getty Images

There's been a sharp decline in the number of arrests and tickets and summonses issued in New York City. Police sometimes use work slowdowns to show dissatisfaction with policies, workloads or contract disputes. Justin Lane/EPA/Landov hide caption

itoggle caption Justin Lane/EPA/Landov

A screen shot of Doug Williams from one of his videos on how to beat a polygraph test. Screen shot/Polygraph.com hide caption

itoggle caption Screen shot/Polygraph.com

Police officers check drivers at a sobriety checkpoint in Escondido, Calif. Lenny Ignelzi/AP hide caption

itoggle caption Lenny Ignelzi/AP

Protesters and law enforcement officers face off during a protest outside the Ferguson Police Department in October. Ferguson police statistics show the department arrest blacks at a higher rate than other racial groups — but that disparity is true for police departments across the country. Charles Rex Arbogast/AP hide caption

itoggle caption Charles Rex Arbogast/AP

Mike Myers is the roving village public safety officer serving southwest Alaska villages including Manokotak. Like many officers in rural Alaska, Myers doesn't carry a gun and often doesn't need one. Martin Kaste/NPR hide caption

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