Yeah, that is also true. I actually really enjoyed how solving the mystery was actually quite difficult (for me at least. I'd be a poor detective).
Finding
Thelyron's abandoned shack with the letters from the conduit and his diary where he says he's responsible for the undead outbreak
was irritating when that opened no new dialogue options with either him or Aureus.
I think it a quest inconsistency bug. Technically, you can discover that he is a culprit before going to the church and characters even say that they should confront him about it, but when they go to his house no new dialogues appear. I think this can be fixed with him dissapearing from his house if you find his documents first. That way you can normally confront him at the church.
Also there was one more inconsistency at the church when the enemy (don't remember which one of them) admitted that it was he who was responsible for 3 bosses - flaming twins, baron and lighthouse monster, even though it is possible that the player haven't even encountered them, so those names mean nothing.