Just as I was about to give a hint as to how the patients in hospitals in Mizobe still end up victims, I realize I haven't posted that chapter yet. D'oh.

They do a thorough break down of their methods in book2, and much of it is foreshadowed enough to be a proper mystery with hints and clues. Since we know the anime/manga, it's more of a howdunnit than a whodunnit, but most parts are in fact solvable mysteries, so you can still enjoy it from that angle!