Maybe he saw the consequence of not taking the dude down would be his demise.
That's a dangerously arbitrary standard...Imagine this hypothetical...a string of armed robberies/home invasions has occurred in an area. Unbeknownst to a traveling salesman the neighborhood is on edge, and the salesman approaches a door knocks, and reaches for his pocket to produce a business card. The homeowner draws, fires and kills him because *maybe he saw the consequence of not taking the dude down would be his demise.* Think the homeowner would be getting off as easily as this cop?