If you are a police officer, and you read of the same violence that others do, and one day you encounter a person - white, black, Hispanic, it doesn't matter - pointing a round cylindrical device toward you, legs spread as though he's ready to fire said device, your first reaction is not, "I bet that's an electronic cigarette he's holding."
Seconds stand between whether someone lives or dies. And as much as we would like to believe cops get it right all the time, sometimes they do not. But are we expecting a behavioral dynamic from the police that we ourselves would NEVER get right if we found ourselves in the same situation?
If a police veteran stumbles upon a terrorist activity about to be committed, and risks his/her life to stop that, they are heroes. But if that suspect was strung out on PCP, the the same police veteran is now a racist murderer.