Question: who killed ume hye rin?
Answer: We learn that it was Yoo Jin's father who is responsible for Hye Rin's death, assigning one of his men to kill her in spite of Yoo Jin begging him not to do so. Yoo Jin wanted to save Hye Rin, but she was too late. She could have saved Hye Rin by calling 911, but she chose not to.