【明報專訊】LAST WEEK in St Louis, Missouri, the US, a grand jury decided against indicting Darren Wilson, a white police officer who had shot and killed a young black man in Ferguson. The decision triggered demonstrations and riots. The generality of black people consider the grand jury's decision evidences unfairness in the administration of justice. In a hundred and seventy cities throughout the US people have marched in protest against racial discrimination and police abuse of force. "It takes more than one cold day for the river to freeze three chi deep." Only if the US authorities face squarely the long-standing malady of police brutality and reform the police's culture and system can they prevent tragedies from repeating themselves.