Los Angeles ? A white former transit officer was convicted of involuntary manslaughter Thursday in the videotaped shooting death of an unarmed black man on an Oakland train platform in an encounter that set off days of rioting in the city.

Prosecutors had wanted Johannes Mehserle convicted of murdering 22-year-old Oscar Grant, who was shot once in the back as he lay face-down.

The jury’s conviction on the lesser charge raised concerns of a repeat of the unrest that followed the shooting on New Year’s Day in 2009. The incident is among the most racially polarizing cases in California since four Los Angeles officers were acquitted in 1992 in the beating of Rodney King.

Near Oakland City Hall, a crowd moaned and cursed Thursday when they heard the verdict, decrying what they called a lack of justice.