It was very likely just lost not stolen. I'm sure the original owner has a new iPhone by now and that particular one will also likely be in the att system as having already been replaced.
Can't confirm any of of that but that's my guess. That said I'd just be upfront with the kid at the local att store and have them look it up. They don't have to know the whole back story just thAt you have a once lost iPhone that you know nothing about and want to see if it can yield you a replacement. I know the guys at our local store would likely do it. No one is screwing the previous owner as by now they likely already have a new phone. Just junk to them.
Can't confirm any of of that but that's my guess. That said I'd just be upfront with the kid at the local att store and have them look it up. They don't have to know the whole back story just thAt you have a once lost iPhone that you know nothing about and want to see if it can yield you a replacement. I know the guys at our local store would likely do it. No one is screwing the previous owner as by now they likely already have a new phone. Just junk to them.