beta
I'm not a novel reader so it's only a theory but I think the bad guy is the white haired doctor who first told J about Sayoung being experimented on.
He's in the middle of everything as he is in charge of the dungeon anomalies but he also seem to know a lot about prometheus and the experiments, I also don't think that there are that many people that knows about Sayoung and for now we didn't really see that doctor interact with other people (he didn't even go to the weapons event and he gave the ticket to J for whatever reason because he barely knew him).
Just a theory for now so if someone's reading the novel is seeing this, please tell me everything you know cause I don't mind spoilers and I need to know.