They should have escorted the man off the property when they fired him. Then locked everything down and let the police know that they had fired a hot head. This is really a shame.
That’s how we handled terminations where I worked. The employee would be taken to the Human Resources office and terminated with several managers and the plant manager present. He/she would then be escorted to the guard shack. Any personal belongings would be brought outside to him/her and at no time were they allowed back through the gates.