Story short ideas, I need help...?

I have this short story idea about a kid who is staying after school for detention. After detention is over he is heads to the bathroom before leaving the school. In the bathroom he slips and falls on some water and knocks himself out for a few hours. When he awakes he is alone in the school and it is night time. On his way out I want him to see something shady with the janitor. Such as maybe the janitor is dragging a student body down the hall and the kid happens to see it. But this idea sounds kinda of cliche...any better ideas for what he can see the janitor doing?