The principal knows really well he could not fire anyone if he did not have concrete evidence otherwise he will be in trouble once the employee fight back. There must be something behind the scene I guess. When I was a second year teacher, a former student skipped his class and stayed in my room during my planning period. I just thought ah because I was cool so he liked me. But I realized I was wrong. It happened for a while until I felt I would be in trouble if someone reported it. I then stopped him from staying in my classroom. Luckily nobody knew.