As far as you got to know, Dragnar did it.
Aerie can tell you that, the gaunt can tell you that, and even you saw it.
Can you look past that kind of framing?
Dragnar slays my servant and then leaves only to immediately walk back in and cry "Who did this?"
Also I'm psychic.
Edit: Astra'ath doesn't know it was xarn. It assumes it was a play by the other gods to destroy Dragnar's neutrality.
Edit2: Also it doesn't matter if he really did it or not, if you think about it. We're in no position to siege the library or attack him for it, so if he's lying then we're better off playing along for now. If he stays neutral, he probably didn't do it. If he throws in with the other gods despite us believing him, he was probably guilty.
Dragnar would not know you had a vision of Aerie being murdered burned into your mind. Would that not seem like a loose piece of the puzzle?
"You say you didn't kill her, but we all saw you. And then destroyed my sword... for no apparent reason? That seems a little fishy."
At the very least I wouldn't trust him anymore, let alone let him join your alliance.
Don't worry, I don't trust him.
Then again I don't trust anyone.
If this war wasn't about to start I'd be gobbling his library right now.
Yes. But the sword was quite strong.
Yep, and I am demanding that he fix what he broke.