Definitely, the pub owner (who was convicted of gambling in the past) is super suspicious. But I've been watching this show with my mom, and from episode 3, she began suspecting the Chul Jin (the partner/subordinate) because she thought he was faking having amnesia.
Then we had ep 6, and now he is somehow connected to the pub owner.
DongMan (professor) told Seonho that the academy would be empty because of the sporting games, and the one person who DongMan happened to run into was his subordinate (who was just suddenly transferred to work as a professor) and Seonho missed finding the culprit who entered his room.
not only that, in the preview for the next ep, we see Chul Jin trying to get close to Seonho (WHY?) but Seonho rejects his advances to become friendly with him (not those sort of advances lol you know what I mean)