We still don't know enough, but we're getting a lot of clues that he was the one who kidnapped Woojoo, and we already know he's behind the person who gave Jiheon the pills. The thing is, we don't know if he's really after Wojoo or if he wants to hurt Jiheon. And with what's happening in this episode, I'm afraid he'll kidnap Wojoo again.
Maybe he hates Wooju for some reason
Wait I might've missed something then, what were the clues that pointed towards him being the one who kidnapped Wooju?
The professor is related to the person who rescued Wojoo and knew about the kidnapping but never told Wojoo himself, and he knew Jiheon long before that. Anyway, I think there were more clues, but I have to read it from the beginning. The fact that he's manipulating Wojoo into believing his hallucinations about Jihyeon are real is also a clue.
GUYS I NEED THEORIES ON THE PROFESSOR WHAT DO U GUYS THINK HIS OBJECTIVE IS CUZ TO HELL IF I KNOW (╯°Д °)╯╧╧