The officer, Jeronimo Yanez, had been charged with second-degree manslaughter and endangering safety by discharging a firearm in the shooting of Philando Castile.

After the verdict, Mr. Castile’s family immediately left the courtroom. When a deputy tried to stop his mother, Valerie, she yelled “Let me go.”

Jurors and Mr. Yanez were quickly led out of the courtroom.

The verdict, which came on the fifth day of deliberations, followed the acquittal last month of an Oklahoma police officer who killed an unarmed black man and, of particular interest here, a prosecutor’s decision last year not to charge the Minneapolis officers who killed another black man, Jamar Clark.