You observe behavior which may be a violation of the law, construed as a threat to people or property, construed as a disturbance of the peace (which includes refusal to leave the library after being expelled), or
A member of the public requests police attention or reports any act which may be a legal violation.
Call 911 immediately. You do not need supervisory or administrative staff approval to do this. Tell the police dispatcher if the perpetrator remains in the library. Describe the perpetrator (e.g., sex, height, weight, skin color, hair color, clothing, automobile make and license plate).
Be mindful of your own safety. Do not risk your health. Do not intervene in violent acts. Do not defy or approach anyone who is armed. Withdraw from violent scenes.
After calling the police, notify administration of the incident by phone.
Summoning the police does not mean you are filing a complaint. The police can resolve a situation in ways not requiring legal action. Tolerating unlawful behaviors can make your worksite less safe and place you at risk of a lawsuit for not responding to a patron in his / her time of need.
Time spent filing reports or serving as a witness is work time.