Found an iPhone

So I found an iPhone we have tried everything to find the rightful owners even paid money to see it returned to rightful owners. The phone is locked to iTunes it’s on a unlocked Carrier Phone service is turned off. So no way to get a phone number we are contractors we technically keep anything that we find As they didn’t pay and trashed the home. However if I did find the owner we would simply ask that he paid for damages to the home. He left tons of stuff behind most we junked but when you find an iPhone that’s pretty serious looks like they only played music off it as it was hooked to a puma speaker system they had it in a drawer in the kitchen how you for get an iPhone idk but my question is how to find owner if there isn’t a carrier and Apple wouldn’t even hook to iTunes like lol I know it was purchased by someone I am trying to talk with them it’s on lost mode I found out that much but it can’t Connect to Wi-Fi unless you agree to guidelines Or most of the time has a password! We had things stolen from us so no way we would steal we could even provide additional information of where we got it.