They’ve been checking under the busses before that incident. It’s a safety precaution to make sure there aren’t any children under the bus.

My uncle was the resource officer working at the school the time of the incident you mentioned. It was a really bad time for him - he had to stand with her body while waiting for someone to show up with something to cover her up AND had to go tell her mother she was killed. It was also the beginning of the school day, so his job was to stand with her body and try to prevent the other students from seeing her… she was decapitated.