Honestly, I started liking EunSeong but my gut tells me not to trust him. HyeMin is a psycho so I expect her to do anything. Also I doubt she is working all alone, because the anesthetic in SeoJun's drink couldn't be given by her since he didn't like her to the point his friends didn't even know about her existence, which makes me believe that EunSeong is still involved in the crime. Also another thing that makes me feel like the killer wasn't working alone was the time Kim Sin U snooped in SeoJun's backpack was when he was examining his camera and we heard someone say "he is so annoying". I don't know if I'm overthinking that small detail but why would they even put it in if it wasn't important, we don't usually hear random characters have lines so why did this one had one?
SinU being the killer is too obvious,it can't be him. Someone could've told him to drop off something to the club room. EunSung is looking extra sus right now, he always follows them around and the fact he didn't consider himself SeoJun's friend isn't really helping his position. The sister is just as sus.