A jury has convicted a white former transit officer of involuntary manslaughter in the shooting death of an unarmed black man on an Oakland train platform. Johannes Mehserle was found guilty on Thursday in the New Year's Day 2009 killing of 22-year-old Oscar Grant. Involuntary manslaughter carries a sentence of two to four years. As the verdict reached the streets, scores of people were arrested in Oakland riots as police tried to wrest control of downtown from looters angry about the BART verdict earlier in the day.