Crime Scene Episode 9

A cleaning lady discovered Shin Young Gwang, a referee with 8 years of experience in the giant league of professional football, in the soccer field goal. Referee Shin Young Kwang had many wounds on his face, and his face was covered with a bloody dust bag, and the assistant referee was held in one hand. The estimated time of death was between 10:00 and 11:00 pm the night before, and the victim's clock was stopped at 10:15 pm. Who is the murder, and what is his/her motive? (Source: namu.wiki)