US officials have released video from a dashboard camera showing a white police officer shooting a black teenager 16 times in Chicago.
Officer Jason Van Dyke has been charged with first-degree murder for killing 17 year old Laquan McDonald last year.
Police use of excessive force against African Americans has been the subject of nationwide protests for months.
Chicago Mayor Rahm Emanuel has appealed for calm in the city.
IN:"I would like..."
OUT: "remain peaceful"
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