Congressional staff members gather at the Capitol to raise awareness of the recent killings of black men by police officers, both of which did not result in grand jury indictments, on Dec. 11. They are joined by Rep. Elijah Cummings, D-Md. (second from left), and Senate Chaplain Barry Black (far right). J. Scott Applewhite/AP hide caption

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St. Louis County Prosecutor Robert McCulloch announces the grand jury's decision not to indict Ferguson police officer Darren Wilson in the Aug. 9 shooting of Michael Brown, on Nov. 24. Cristina Fletes-Boutte/AP hide caption

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Melissa W. Green, right, and her daughter Reshae Green holds up their signs at Freedom Plaza during the "Justice for All" march and rally on Pennsylvania Avenue in Washington on Saturday. Jose Luis Magana/AP hide caption

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Black congressional staffers hold their hands up as they pose for a group photo during a walkout on on the steps of the U.S. Capitol Thursday, in a protest over the Eric Garner and Michael Brown cases. Alex Wong/Getty Images hide caption

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Protesters light a dumpster on fire, early Monday in Berkeley, Calif., as raucous demonstrations hit the streets of California for a second straight night in response to police killings in Missouri and New York. Taylor Nitta/AP hide caption

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A man carries a box of merchandise from a vandalized Radio Shack on Sunday during a march against the New York City grand jury decision to not indict a police officer in the death of Eric Garner, in Berkeley, Calif. Stephen Lam/Reuters/Landov hide caption

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People stand in prayer after marching about a mile to the police station to protest the shooting of Michael Brown in Ferguson, Mo., in August. Charlie Riedel/AP hide caption

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A protester flees as police officers try to disperse a crowd comprised largely of student demonstrators during a protest against police violence in the U.S., in Berkeley, California early Sunday. Noah Berger/Reuters/Landov hide caption

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Protesters hold caskets as they march across the Brooklyn Bridge for the second night in a row following a decision by a grand jury not to indict an NYPD officer involved in the chokehold death of Eric Garner in New York. JOHN ANGELILLO/UPI /Landov hide caption

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Ferguson police officer Darren Wilson, shown during his medical examination after he fatally shot Michael Brown, has resigned from the Ferguson Police Department, the AP reports. Wilson has been on administrative leave since the Aug. 9 shooting. AP hide caption

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Youths walk past a mural calling for peace in Ferguson, Mo., on a building up the street from the city's police department a day before the grand jury decision was announced. David Goldman/AP hide caption

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Members of the National Guard detain a protester in Ferguson, Mo., on Wednesday. More than 2,000 National Guard troops spread out across the St. Louis area to prevent another night of rioting and looting after a grand jury declined to indict officer Darren Wilson in the fatal shooting of 18-year-old Michael Brown. Adrees Latif/Reuters /Landov hide caption

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A local business is boarded up in anticipation of another night of unrest in Ferguson, Mo., Tuesday. A day after people set fire to buildings in the city, President Obama said, "I have no sympathy at all for destroying your own communities." Michael B. Thomas/AFP/Getty Images hide caption

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A police officer in Ferguson, Mo., stands guard as protests turned violent following Monday night's announcement of the grand jury's decision not to indict police officer Darren Wilson in the shooting death of 18-year-old Michael Brown. David Goldman/AP hide caption

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Missouri Gov. Jay Nixon said that parts of Ferguson were "a heartbreaking sight" Tuesday, with residents afraid to go outside. Justin Sullivan/Getty Images hide caption

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