Does it have a carrier brand on it? Did it have a sim card in it? From what carrier? ATT? TMobile? You could take it to that carrier's store. They can find the owner. The sim card could be placed in another phone and the phone number retrieved. Perhaps there are numbers stored on the sim card?

There are lots of things you *could* have done and still can. At least the owner was smart enough to password protect it so dishonest "finders" don't get their data too.