I eventually remembered that the guy who mugged Jamie turned out to be a black MINOR. Wallace's brother or other relation I am guessing, seeing as he appears to have heard a version of the story along the lines of "Jamie started the fight for no reason". If I recall, that was the authorities conclusion more or less, that they had no evidence to show Jamie was the victim not the aggressor?
I tend to withdraw a bit when the word "nigger" comes in to play (hate the word), but it's useage here is effective in conveying that Wallace seems to have the idea the attack was racially motivated...