I honestly don't believe I could. I mean, if just reading that made me feel uncomfortable, I doubt I would be likely to do it in a real life situation. It's not a question of morality or even logic with me, I just really don't think I could. But I suppose we never know what our instincts will tell us to do in such a situation.
I guess it would also depend on what my circumstances are in the future. If this happens in, say, a warzone or something, I might be more desensitised to death and more likely to do it, but if it happened randomly here in the suburbs, it would be far more jarring, and I think I would just be too stunned to think, and wouldn't be able to act. Also, I suppose if I was older and had a wife and kids, that would change my decision.
But, as of right now, if it happened this very second, then no; I couldn't kill someone. I don't have that in me.