1x7 - Who Killed Daigoro Tokuyama?

Daigoro Tokuyama appears in the classroom! The students scream, but Yurina Hirate notices that it's a different person. His eyes are too clear, and he's too clean. "I don't think Daigoro is alive anymore," the man says. He had come to the school to investigate because Daigoro had called him about some trouble at school. So, who killed Daigoro Tokuyama?