In Season 1, Part 1, Dong-eun sends Myeong-o to pressure Yeon-jin into confessing to killing her previous bully victim. Myeong-o asks to meet with the bullies and is then killed by an unidentified attacker. Yeon-jin seems to be the murderer based on the evidence.
One of Yeon-jin’s past victims, Yoon So-hee, passed away in high school after falling. Although her family is still doubtful, her death was determined to be a suicide, and her corpse has been held in the morgue. Given that Dong-eun saw So-hee fall and discovered Yeon-jin’s name tag in her hand, it is possible that Yeon-jin was involved in her death.
