"I have already explained myself on that count," Snape said, sounding bored. "I could do so again, but it would only tire us both. In the end, when I have orders to kill someone, I do it." He shrugged. "I'd have done it sooner, if it had in fact been my duty. For reasons only known to Him, the Dark Lord chose to give it to someone else. It was hardly my place to tell Him He was wrong."