I think jinwoo killed his own parents but he's in denial that he actually did it so his subconscious made him blame their death onto gunwoo or whatever
I don't think so cuz he's got no reason to do that. He seemed to really like his dad and judging by how Guwon killed multiple people cuz they were "useless" to him, it seems more likely he did it
I think jinwoo killed his own parents but he's in denial that he actually did it so his subconscious made him blame their death onto gunwoo or whatever