The Wind in the Box: the Unfinished Building in the School

A corpse with a strange death shape was found in an unfinished building that had been closed for many years. The corpse was covered with scars and was kneeling on the ground, as if atonement... After investigation, it was found that there was a psychology lecture taking place in the teaching building a few hundred meters away at the time of the incident, and everyone participating in the lecture was suspected of committing the crime. However, how did the murderer complete the round trip and kill people within ten minutes from a distance of several hundred meters? Intention: None