Los Angeles Police Capt. Andy Neiman announced in March that a knife possibly linked to the murder of O.J. Simpson's ex-wife was undergoing forensic tests. Those tests have determined that it was not involved in the crime. Nick Ut/AP hide caption

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Nick Ut/AP

Baltimore City State's Attorney Marilyn J. Mosby announces that criminal charges will be filed against Baltimore police officers in the death of Freddie Gray in Baltimore on Friday. Gray died in police custody after being arrested on April 12. Andrew Burton/Getty Images hide caption

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Andrew Burton/Getty Images

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

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Alex Matzke for NPR

Open Cases: Why One-Third Of Murders In America Go Unresolved

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This undated photo taken from the Kaufman County, Texas, website shows Kaufman County District Attorney Mike McLelland. McLelland and his wife were found killed in their house on Saturday. AP hide caption

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