Responses
He did for sure cause some of their deaths, but as far as we know he never directly stabbed someone or something like that, just helped with their "accidents" when the opportunity presented itself. Based on other characters' statements it's pretty clear he is responsible for their passing to some degree.

im kind of confused about Dohun being a murderer. I know he technically didn’t kill all of those bullies in high school but didn’t he kill at least one? Or was that another thing yuwon misremembered idk im lost