as an objective observer watching the video you had a much better idea of what was going on. hell, you were even warned before clicking on the video what was going to happen. the people on the scene probably didn't even have enough time to process what he was holding was a gun and what he was trying to do with it before he shot. even those who did probably only had about a second before he actually fired the gun, and they were likely frozen from being too stunned/afraid of the fact that someone that close to them was trying to kill someone with a gun.
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which one's green, broccoli or cauliflower?
http://i.imgur.com/XxFPf.jpg