I think you should have drained your savings account paying a private detective to track down the original owner of the Kindle, or maybe a psychic. Amazon doesn't want it... cops don't want it... yep, you should have gone with a psychic private detective at your own expense. Any other decision shows a horrific lack of judgement.
There probably is no "owner," pining away for his stolen Kindle. Amazon doesn't always require the return of a Kindle when they exchange them. People are scamming Amazon all the time with "Mine never got delivered" or "It just didn't work when it got here." Amazon writes it off, blacklists the serial number, and then that blacklisted Kindle gets sold to some poor unsuspecting (or suspecting) schmuck. The "owner" was probably the crook... and Amazon, in their own way, are encouraging a Kindle black-market by not
requiring returns of "defective" units instead of asking people to "pretty-please dispose of them properly."