1. It is not understood as to when you want to retain the said employee, why do you want to file FIR against him.
2. Actually, he was not supposed to join a new Company without being released from your Company.
3. However, if the matter goes to court, you might also be questioned as to why did you not release him when he had resigned during his probationary period.
4. Please note that he has a civil right to work or not work with you and you can not refuse to release him without showing any valid reason when he was in his probationary period.
5.Moreover, no Criminal Case stands here and at most you can conduct a disciplinary proceeding against te service conduct rule of your company and terminate him from his service.