There are many possible answers to this question, and it depends on the details, but if they are unwilling to give it up you can likely sue them for conversion (theft) and/or replevin (claim and delivery). Under replevin, the judge can order the person who is holding the property to hand it over to the Court, or even the Plaintiff in some cases, until it can be determined who who rightfully possess the property.
I would need more details to determined whether you can file the action in Nevada or not. If this is something of great value to you, I recommend that you consult with an attorney to pursue it.
*Disclaimer: This answer does not, nor does it intend, to create a client/lawyer relationship. Furthermore, it is strongly recommended that you consult with an attorney before acting on the above advice.