Like Quin said, the question pre-supposes that I want to kill the person. So, if I definitely wanted to kill them, and there were no repercussions, then I definitely would. To really explore the question I think you need to get rid of, or restate, the "want" part of it.

I don't think I'd ever be in a position where I, in every sense imaginable, would want to kill someone. I can't morally justify asserting my own existence and simultaneously deny someone else's. Even if I were to take a consequentialist view, in which killing one person will almost certainly benefit others, I think I would question that action for the rest of my life. Not knowing whether or not it was right would be a punishment on its own, at least in my mind.