Okay, i see there is a problem. I feel sad for that this can happen.
Technicaly there was no theft at all, the player took what you give him the permission to take it and use it.
I don't want to blame you for this, but we are on the internet. We ar anonymous. And anonymous people do terrible things to anonymous poeple.
The only way to be sure you can trust a person is a personal connection to this person.