I really believe hes not a bad person. Thinking about the murder, my guess is that it was selfdefense (considering the head of the village was probably the one that approved the exorcisms so atacking Hyun So woundnt be that odd), an accident or he just feel guilty somehow. Maybe he was his father culprit? If he really killed his father so he would stop killing people, maybe he knew who was his partner too and was attacked by him or decided to really prevent killing them both?
Anyways, he freaked out really bad when he almost killed that other guy in the woods. And he was being hunted. It was a kill or be killed kind of situation. He was lucky the guy got scared, otherwise he would be dead by now. He is actually really scared of being like his father and hurting people. He jumped in front of Ji Won to save her and even when he had kidnnaped Moo Jin all he has done was treatning him (really funny tho) until he got scared as shit. I dont think he was actually going to hurt him.
Besides, psychos are unable to take care of lifes that are more weak than them. HE HAS A DAUGHTER. Who hes taking care amazingly actually.
Plus teory: His father ghost or whatever maybe is afraid of Ji Won because he gets more human around her? The first time he disapeared was when Hyun So was in the rain and he smiled without realizing. When he did, his father ghost vanished out.