You can have the wallet since you find it but you can never own the money/coins inside since you don't have the keys that will open it. Therefore, it was useless to find it, you don't have any benefits as you can never use that wallet. If I were you, better make your own wallet to have full access rather than claiming that the found wallet is yours. You can legally claim it was yours when you have the keys that is the way to prove ownership. Otherwise, cour claim id invalid and just a waste of time as we can never get anything that is inside.