After the final exam, a body hanging in the men's restroom on campus could not be confirmed as suicide or homicide, leading to five suspects who stayed in the school. Was it a homicide? There was no sign of homicide on the body. Was it suicide? The feet of the body were a full 30 centimeters away from the ground, and there was no footrest within reach. The criminal police unraveled the problem and found the bullying problem in the class and the interpersonal relationships that gradually surfaced. The class teacher who was well-liked by students and trusted by parents; the class monitor who had a strong sense of justice and was brave enough to fight for the bullied classmates; the gifted students who only cared about themselves and watched the bullying happen coldly; the cowardly male students who echoed and followed the trend; the bad students who were rich and powerful and held a leadership position in the class. Some had motives but no opportunities, and some had opportunities but no motives. In the almost empty campus, who was the one who hung the water pipe on the neck of the deceased?