Wilson may or may not have known about the robbery when he first confronted Brown. There have been contradictory reports on that point. But Brown knew about it and undoubtedly believed he was about to be arrested for it.
Regarding what was known by Saint Mickey and not known by the officer:
http://www.lawofficer.com/article/lifeline-training/open-letter-captain-ronald-s-j
Appropriate to consider when we hear those that should know better say we should not consider the robbery as part of what happened a short while later.