Dozens of people protested this Friday on the streets of St. Louis (Missouri) after a judge exonerated Jason Stockley, a white policeman who killed in December 2011 Anthony Lamar Smith, a black man who suspected he was a drug trafficker and persecuted With your vehicle. Police used tear gas to disperse protesters after they tried to block a city street. At least four police officers were injured in clashes with the demonstrators, according to the police. The authorities arrested 13 people. Some of the protesters were armed with rifles, according to photographs of the local press. Stockley is the umpteenth case in the United States in the last years of police officers who are exonerated in African American deaths. San Luis is a key place in the U.S. debate for the treatment of police and justice to blacks. Death in August 2014 in Ferguson, a suburb of the city, Michael Brown, an unarmed young Negro, at the hands of a white agent unleashed intense protests and opened a national debate on police and race. Among the demonstrators this Friday, was Brown's father. A judge considered that Stockley was not guilty of a first-degree murder offense and that he might act because he felt threatened. Smith died in his car after a police chase. The agent Descerrajó five shots through the vehicle window. He alleges that he acted in self-defense and believed that the suspect had a gun in his car. But the prosecution accused Stockley of putting a gun inside the vehicle to make it look as though it was Smith's when in fact only DNA traces of the police were found. According to some recordings, the agent was heard saying that he was going to kill that son of a bitch, referring to the suspect.