I'm a librarian who loves anime, manga, and reading a wide variety of genres.
[ETA - I figured I'd add this: absolutely don't click my spoiler tag unless you don't plan to read this. I don't actually give away who did it, but there are spoilers in my wording.]
Finished! I can now say that, no matter how long I sat down and thought about the clues, I'd never have figured everything out. As it was, I managed to correctly guess 1.5 things, sort of:
(show spoiler)
The actual explanation made sense, although it relied a lot on luck and the police either missing key details or being unable to get key information. And dang did the killer have to be ice cold.
I wish the second book in the series, The Locked Room of Pythagoras, were available in English.
Oh, and I'm going to be counting this for my Locked Room Mystery square. I haven't done a Bingo update in ages - I need to do that when I get home.