

They had no requirement to identify themselves to campus Public Safety Officers. PSO’s are not police. Locking them in the building is clearly unlawful detainment, and must invalidate any trespass charge as they were prevented from leaving (to be guilty of trespass you must first be notified and then remain in spite of being allowed to leave). Reasonable force is aboslutely an appropriate response to unlawful detainment.
If you prevent them from leaving at any point you invalidate the accusation of trespass.