“Of course the grease is real,” the thing replied. “It’s not inside men, not like Francis thought. It certainly wasn’t in Brandon. And it was never in your father,” it added, “although he thought it was. That was awfully useful for Daphne. It was so easy for her to keep him in check. All she had to do was tell him that he was acting unclean, and he’d go do his penance.”
So she was the one who drove him to kill. Was it her delusion influencing him? Honestly, that whole family is screwed up ...