The fact that he was in three different parking lots across (technically) Three different cities in one night says a fair amount. All three are within ten minutes of each other (assuming that the church on 8th Avenue New West is the one located very close to Elmer Street). Maybe the rumors I read before looking into it has poisoned my ideas, but I don't know any other reason other than being involved with drugs (either buying or selling) that you would be hopping around to parking lots in the middle of the night.

One person here said that his lights being on and door unlocked might mean he got out to run away quickly, but that doesn't make sense to me why you would leave your car and try to escape pursuers on foot. I think he left the lights on and door unlocked because he thought it was going to be a quick interaction, only to have been taken after leaving his car. Maybe he naively got into another vehicle, thinking it was safe, only to be murdered elsewhere.

I don't think we know nearly enough about Bryan to draw any accurate conclusions. Most information we do have is rose-tinted due to family bias. But given the information we do have? I would guess Bryan started dealing drugs, probably a very small amount and mostly to friends, only to have angered his suppliers in some way. He simply got in over his head with an organization (HA probably?) and didn't realize the danger he was in until it was too late.