The fatal arrest of a black man who complained of suffocation as a white police officer knelt on his neck plunged the U.S. city of Minneapolis into chaos this week and sparked nationwide protests.In Minneapolis, furious demonstrators set a police station ablaze on Thursday, the third day of violent protests that have now spread to the Minnesota state capital, St. Paul. Other buildings in the area were also torched. So was a car. A discount store was looted.