Why is it a conflict of interest though? As the prosecuting attorney for St Louis, I can guarantee that he has likely been involved in cases involving the members of all races. If he has been cited for unfair treatment towards black defendants previously or some sort of conspiracy to with hold or manipulate evidence towards black defendants, I could see where there may be a point here. But from my understanding, someone hasn't been able to point out a specific part of his case history that indicates he may be holding some sort of bias.
If I'm wrong, I'd love to be corrected.