ST. PAUL (AP) - A Minnesota prosecutor says he won't step aside for a special prosecutor while considering charges against police in the slaying of a black motorist, but he's adding one to his team.

Ramsey County Attorney John Choi said Friday that he was elected to uphold the law and intends to do so during the investigation into the July 6 death of Philando Castile. But he says he'll "incorporate" a special prosecutor to enhance trust in the results.

Choi named former U.S. Department of Justice attorney Don Lewis to that role.

The 32-year-old Castile was killed by a St. Anthony police officer during a traffic stop. Video of the immediate aftermath was streamed live on Facebook by Castile's girlfriend, who says Castile was reaching for his wallet when he was shot.