If he is a probationer, then he can be removed without cause (at least most appointments are on those terms)
So I have no idea why you wish to create problems for your self in putting details and casting aspersions on the person in the termination letter. Why not just have a simple termination as per terms of the appointment letter and close the matter.
If you are doing something out of spite, then yes, you will have to face the music.
In such cases, you better follow Dr. Siva's suggestions