How exactly is one supposed to know the bad guy is wearing a bullet proof vest before you engage him? What if I left my x-ray vision goggles at home that day? If I feel I need to engage, my first shot will be center mass. A vest or drugs may mean that shot has little or no effect. I won't know until I get there, but the first shot will be center mass.
I do have my doubts about the gear he was wearing. The initial reports of the Denver movie theater shooting reported a "bullet proof vest" as well. The article I read about the Oregon shooting that mentioned the bullet proof vest was also kind enough to point out that the AR-15 rifle that was reportedly used was a civilian version of the M-16 fully automatic rifle used by the military.
I can only assume the reporter is a little long in the tooth since the M-16 hasn't been fully auto since Vietnam.