St Paul - A Minnesota prosecutor said on Friday that he won't step aside, but will add a special prosecutor to his team while deciding whether to charge a police officer in the fatal shooting of a black motorist whose girlfriend recorded the immediate aftermath of the shooting in a live video on Facebook.Ramsey County Attorney John Choi said he was elected to uphold the law and intends to do so when investigating the July 6 death of Philando Castile. But he said he will "incorporate" a special prosecutor into his team to enhance trust in the results.Choi named former US Department of Justice attorney Don Lewis, who is black, to that role. The former law school dean also helped investigate allegations of excessive force in the arrest of a black community activist in 2014 in Minneapolis. In that case, Lewis wrote that the officers were justified in the way they handled the arrest."This independent perspective can only enhance the integrity and legitimacy of our decision in this case," Choi said. "This is ultimately what justice requires."An attorney for the Castile family did not immediately respond to an email seeking comment.Castile, 32, was fatally shot during a traffic stop in suburban St Paul. Video showing Castile slumped over in the driver's seat, his shirt soaked with blood, was streamed live on Facebook by Castile's girlfriend, who said Castile was reaching for his wallet when he was shot by St Anthony police officer Jeronimo Yanez.Gun, not raceAn attorney for Yanez, who is Latino, has said the officer reacting to the presence of a gun and not Castile's race. The attorney also has said that one reason Yanez pulled Castile over was because he thought Castile looked like a "possible match" for an armed robbery suspect.Choi said he hasn't yet been presented with the results of the investigation into the shooting by the state Bureau of Criminal Apprehension.Choi also said he had not yet made a decision on whether his office will make the charging decision or if he will send the case to a grand jury. Activists have urged him to avoid a grand jury, arguing that they rarely charge officers and their process is hidden from view.Protesters have demonstrated repeatedly since Castile's death, often outside the official governor's residence in St Paul. Nearly 70 protesters were arrested this week as police attempted to clear the street in front of the residence.Lewis, the special prosecutor named to help in the case, is a former law school dean at St Paul's Hamline University. He has spent much of his career in private practice at a law firm he co-founded a group that focuses on defending corporate clients. He was hired by the city of Minneapolis to investigate allegations of excessive force in the activist's 2014 arrest.