Manhandling employee with help of outsiders - process of action to be initiated & the steps to insure smooth functioning

Dear All, Two of our employee (1st is on-roll & 2nd is contractual) had a fight outside the office premises in night. They both parted their ways from the location & the 2nd employee (contractual) came at office premises at midnight with some local goons to take revenge from 1st employee. Goons have threatened to damage company property if he is not handed over to them.
The 3rd employee (on-roll) who was no where involved in the case got beaten up by the local goons for trying to stop them form damaging company property.
Kindly guide me with process of action to be initiated & the steps to insure smooth functioning?

I believe the best way to go about it is to investigate internally about the entire scenario and collect any possible people, video and audio evidence for the entire scenario, especially the assault on your employee and take it immediately to the police and the judiciary as it is something that threatens the life and property of someone in your organization.
Assault and threat of assault are criminal charges and must be dealt with in that severity.