This slightly different use case has probably been discussed here before, but I think it also belongs in this thread.

I struggle with what it means to own private keys.  I think we just "know" the private keys.  Anyone who knows the private key has complete access to the associated bitcoin.  So if I try some obscure brainwallet phrase and discover a long unattended address with BTC, is this the same kind of theft as the OP's fraud use case?

Since we can't communicate a warning shot to the person who set up a bad brainwallet passphrase, how can any be sure that the private keys have not been lost due to bad memory/security proceedures?  That might be the same thing as finding a $20 bill in the middle of Central Park in NYC. Untraceable owner and no confidence that the authorities can get the money to the rightful owner.  Most people would treat it as a windfall, and no one would consider it theft.  I think this last point depends on the amount of money found -- if you found a satchel of $100,000 cash, taking it to the authorities would make sense.

But back to the question of "knowing" vs. "owning" private keys.  Can there be clear delineation of how to interpret this?