I do not understand what exactly you require. Do you require a draft of a termination letter, or do you want a letter to be sent to the company where you suspect him to be employed?
If you want clear proof, then I suggest that you send a letter stating that you have selected the person for employment in your company and you require feedback from them for your records. Indicate details like Date of Joining (DOJ), designation, Date of Leaving, and last drawn salary. If they respond based on the information, you can terminate him. If they do not respond, then make a call and ask for information regarding him and try to record the conversation. If they do not employ him, then there is no question of taking action.
Regards,
Sivasankaran