OP can't know if the private key is valid without trying to import it into a wallet, which he shouldn't do because he would be compromising the security of the coins. He could try to sign a message with the keys but that would again require that he plays around with the private key. Better not do any of that.

You are being very weird about your definition of finding. You can find a mushroom in the forest and take it and probably no one would care. You can't find a bike leaning on a tree or a wall and say I found it so it's now mine. I didn't steal it from anyone, it was just there when I was walking by. Finding and not taking it or not keeping it for yourself is totally different from finding and stealing an item. 

I can only agree with what o_e_l_e_o said. Without knowing much about Bitcoin, why do you think you have the skills, knowledge, or experience to identify the right person that can help you in your quest?