Issue him a notice to report on duty as he has been remaining absent without intimation and/ or prior approval which is in violation of company's policy/ rule (assume there is explicit policy/ rules in this regard) applicable to you. If you don't report by.....(give a specific date) it will be assumed that you have relinquished the employment and management will take appropriate action in this matter.
Action for his misconduct of physical assault on colleague may be dealt separately once he reports.
At this stage, you may order domestic enquiry to investigate the incident. First, design the terms of references for the enquiry and decide who will conduct the enquiry. After that send an official letter to the delinquent employee to depose before the enquiry. In the letter, write clearly when an enquiry will be conducted, where it will be conducted, who will conduct it etc. Send the letter by RPAD.
If the delinquent employee fails to depose before the enquiry, order the enquiry once more after a one month period. If the employee fails to depose second time also, you may take action ex parte and terminate his services.
Larger issues: -
What I have outlined is only the administrative procedure. Nevertheless, there are larger issues to be looked at. As of now, the focus is on the individual but at the same time, we need to give our focus on the organisation.
Why things have come to such a pass where an employee had to resort to physical assault? He has not just physically assaulted but abandoned duties also. This shows his extreme frustration. Why was he frustrated?
For how long the tension was brewing? Why it went unnoticed by HOD and if noticed, what steps did he take to resolve it amicably? Overall, what is the interpersonal environment in the company? If not physical then is a verbal attack a common feature in the workplace? Has any training been conducted on fostering a healthy interpersonal environment in the company?
What about the employee in question who attacked his colleague? Was his behaviour abrasive? Was he irascible? Did anyone counsel him earlier? If yes, then was the counsellor professionally trained?
While it is easy to blame the delinquent employee for his unprofessional behaviour, such incidents erode the credibility of the organisation in the eyes of the employee. These incidents also vitiate the organisation's culture. Therefore, steps must be taken to nip such incidents in the bud.
In all likelihood, he will not return to work nor present himself for any enquiry.
What options you have?
You can treat him as absconding employee after writing to him 2/3 times to resume duty and his failure to do so. As a consequence of this strike out his name from the muster and don't pay his dues or give him service certificate.
This action will serve befitting action for his aberrant behaviour- Absconding and slapping his colleague
But if you are serious about teaching the culprit some lesson, try lodging case of assault by the aggrieved employee and manage to send police at his residence for police enquiry. This might certainly work to straighten the delinquent.
My comments on the last paragraph of your post.
You have advised lodging a police complaint about slapping a colleague. I am a little surprised at your suggestion.
Workplace fracas happens everywhere. To enforce an environment of discipline in the company, initiating disciplinary action is also fine. Nevertheless, lodging a police complaint about a slap is stretching a matter unnecessarily. For the investigation purposes, police personnel may visit the company premises also. What other employees will think when police visit their company?
Suppose if a police complaint is lodged, what will happen? Police personnel will start their investigation and may you know that they take their sweet in filing a charge sheet. For a slap, it will be nothing but huge wastage of time. When the case comes for hearing it will take years for the court's verdict. What company will achieve by doing all this?
Yes, we should show empathy for the victim but lodging a police complaint is not required. The objective of running a commercial enterprise is to satisfy customers. For this healthy work environment is required. The objective cannot be taking on delinquent employees or settle a score with them.
These are my views.
If you care to read correctly, my first preference of action is on the lines proving him absconder.
Second part is only suggestive to create some fear in his mind and not to see its end. Besides the complaint has to be lodged by the aggrieved if he chooses to and not by the company.
Your advice of conducting domestic enquiry will turn out to be farcical as to believe that the delinquent will attend the enquiry is the remotest possibility since he has made up his mind to quit.
You have misread my say and commented on things not meant by me.