You cant call them culprit, because you are the one who lost it :)

If you have activated FindmyiPhone/iCloud, then you can locate (approximate) and erase all your contents and lock the device, so it would be useless for them. but that's possible only if you have activated this feature.

Or if you have IMEI number of your device, you could lodge a complaint with police, they might be able to trace it for you.