The head of the Chicago Police Department has been fired amid widespread criticism over how authorities responded to the fatal shooting of a black teenager by a white police officer last year. Mayor Rahm Emanuel (D) said he formally asked Garry F. McCarthy, the Chicago police superintendent, for his resignation on Tuesday morning, a week after video footage of the shooting was released and the officer was charged with murder. While Emanuel said he had “a lot of confidence in the work” McCarthy has done in Chicago, he said the move was necessary to rebuild public trust and confidence in the police force.