@Kimin,
In the novel, Alberton is actually one of perpetrator.
He, along with the hired muscles from the church and Duke Heinreich's men ambushed the party, killed and mutilated shuli's body.
I think the manhwa change a bit.
Alberton, knelling in shock, probably realized he is cause of it.
Since he told the secret journey to the acolyte.
And with the information, the church made the move.
Also, this also related to Ohara, cause she definetely told her father, that shuli decided to leave after the conversation.
So the church and the duke conspired to had her killed.