FIR for un-authorised access of his email

A was under custody, his email and password was mentioned in FIR, C obtain copy of FIR and use email ID of A and stolen a scanned documents from A’s email account during his custudy, after few month C produce said stolen document in other court and obtain a order for allowing of photocopy of allege cheque as evidence…. after trail A & others acquired… now question is A want to lodged FIR for un-authorised access of his email and stolen of docuement what procedure he should adopt