Have you tried to verify that the private key is real and that you haven't been pranked or tricked into believing that you magically became richer overnight?
That's evil, lol 
Even better it's BIP38 encrypted, someone will be searching for a very long time.Quote
One of the ways to check the genuineness of a private key is to try to spend coins from the address (transfer them to the wallet you control). Alternatively, if you don't want to get in trouble because of someone accusing you of stealing someone else's property, you can simply sign a message with a paper wallet's address and private key. This way, you will verify that the paper wallet is real and that you're not wasting your time trying to find the owner.
No need to sign a message, all you need to do is check if the private key generates the funded address. Even better if you do this offline, for instance using an offline Tails DVD to run Electrum.