It has been reported that a police report said that Wilson was responding to a police dispatch of a suspect in a robbery.
But later in the day, it has been reported that police chief Jackson said that Wilson did not know that the teen was a suspect in the robbery.
I believe this has been explained a couple days ago. Wilson heard a dispatch about a theft, but did not know that Brown was a suspect when he told him to get out of the street. There was someone saying that he saw the cigars in Brown's hand and realized that he may have been the guy mentioned in the dispatch. We will find out at some point when the investigation is complete.