Moral quandaries like this are so fascinating. Sure, he was a terrible person, but after being effectively lobotomized, is he still the same person? If not, then it isn't fair for him to be treated this way, and yet he still committed that unforgivable act.
Wow. This has got to be one of the most thought provoking manga I've ever read. It's been ten minutes since I finished reading it, and I've just been thinking about it. It's a very good manga.