U.S. President Barack Obama addresses a press conference during the second day of the NATO Summit at the Polish National Stadium in Warsaw on Saturday. Mandel Ngan/AFP/Getty Images hide caption

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Members of the Living Faith Christian Center congregation sing a hymn at a prayer vigil for Alton Sterling on Thursday. Sterling, 37, was shot and killed on Tuesday outside a convenience store where he was selling CDs. Gerald Herbert/AP hide caption

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Diamond Reynolds, the girlfriend of Philando Castile, is consoled as she talks about his shooting death with protesters and media outside the governor's residence in St. Paul, Minn. Jim Mone/AP hide caption

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About 200 people gathered outside the Minnesota Governor's Residence in St. Paul on Thursday, protesting the fatal shooting of a man by a police officer. Philando Castile was shot in a car Wednesday night in the St. Paul suburb of Falcon Heights. Jeff Baenen/AP hide caption

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The Triple S convenience store was the scene of a shooting shortly after midnight Tuesday — and the site of protests later that day, after video of a police-involved shooting circulated. Google Maps/Screenshot by NPR hide caption

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Police stand guard during demonstrations in reaction to a Cleveland police officer being acquitted of manslaughter charges on May 23, 2015, in Cleveland. Ricky Rhodes/Getty Images hide caption

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Los Angeles Police Chief Charlie Beck speaks as his department releases a broad use-of-force report Tuesday. The report says that when LAPD officers fire at suspects, their targets are disproportionately black or mentally ill. Amanda Myers/AP hide caption

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Criminologist Joseph Richardson is skeptical that the federal government alone can solve the data problem for police shootings. "There has to be a more pioneering, innovative approach to doing it," he says. Spotmatik/iStockphoto hide caption

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Cleveland police Officer Michael Brilo and other officers have been fired over the fatal shooting of the occupants of a car in 2012, seen here in a photo taken by the Bureau of Criminal Investigation. John Kuntz/AP hide caption

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City Marshals Norris Greenhouse (left) and Derrick Stafford are seen in their booking photos provided by Louisiana State Police in New Orleans. They were arrested Friday on charges of killing a 6-year-old boy and critically wounding his father during a car chase. Reuters /Landov hide caption

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This undated photo provided by the Harris County Sheriff's Office on Saturday shows Shannon J. Miles. Prosecutors in Texas are charging the 30-year-old man with capital murder in the killing of Darren Goforth, a sheriff's deputy who was gunned down from behind while filling up his patrol car at a suburban Houston gas station. AP hide caption

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Brad Miller was fired from the police force in Arlington, Texas, on Tuesday, after the department's chief said he was troubled with how Miller acted in the fatal shooting of an unarmed black man Friday. Reuters /Landov hide caption

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