I also figured out who the killer was, but I honestly never felt that any of the other characters were developed enough to be a plausible alternative; the only other option was >!the wife, or possibly if the daughter had done it accidentally or something, but I can’t see JKR writing something like that because of the social implications.!<
I was literally looking for good books on both cannibalism and the french revolution last year and couldn’t find what I wanted, and these sound exactly right. I eventually gave up, but better late than never.