Everything that's been going on, from what's happening to Eco, how there seems to be some sinister presence behind the scenes, and even the killer himself, it's making me wonder if something supernatural is going on.
Signs seem to be pointing to that, in my point of view, how the killer might actually be some regular guy that's possessed by some malevolent cosmic entity that's killing people just for the fun of it.
I could be wrong, but the being with red glowing eyes, the disturbing visions and sounds Eco is experiencing, all of it seems to be going into some kind of eldritch Lovecraftian territory, and if it's to unsettle the reader, then well done because it's certainly unnerving me.