>I've seen the evidence of the texts in question. Is this smartphone? If so, ensure its not a rooted device, where users can insert/delete things as they want.

>I've seen the evidence of the texts in question. Is this smartphone? If so, ensure its not a rooted device, where users can insert/delete things as they want. -- Let me add another view. Involve HR and talk to him first. If he admits truth then ask him to resign. If he didn't accept, listen to his version of story and ask him for proof. Then decide.