Have you ever issued him a warning letter in this regard? If no, you must do that without wasting time.
In addition, what terms in this regard you are using in Appointment Letters?
Is that if any employee found with any misconduct or overrule the policy and conditions of employment cant be terminate before offering one month notice period or salary as the compensation? Im sure there was nothing stated like this in the appointment letter and your Policies in this regard.
First, you must read the copy of appointment letter that has been issued to him, use the terms and issue him a warning latter finally by stating the reason and if he still not respond or reply issue im Termination Letter without taking much time. Also your policies stated all the things that you have to consider and need to take action, therefore, I second the members above, would suggest you that any employee with this kind of act and attitude must not be allowed to stay more, but you have to your work in a professional conduct accordingly.
Although the reason for termination already communicated by you and he has shown, there is no need to go through a step-by-step analysis of the documentation supporting the reason for discharge.