I'm curious about something. A hypothetical situation. If Ben was asleep while the coins were being sent to his wallet, which was stored in an encrypted file on his computer, and when he woke up, he couldn't remember the keys for decrypting that wallet file, would he still owe the sender the bitcoins?
I would say no.
In this case, I would argue that he never had possession, and thus never had an opportunity to return them to the rightful owner. By statute, and by common sense, in this case the theft wasn't the reception of the coins, but the willful failure to return them.
On the other hand, if they ever moved in the future, I would expect the defendant to end up back in court for theft, and possibly perjury. No problem with the statute of limitations, because again, the crime happens when the defendant has an opportunity to return them, but fails to do so.
This all just comes back to the fact that the anonymity means there's a lot of deniability, and it puts the onus on the sender to make sure they're not sending their money to the wrong place. You're not sending bitcoins to a
person, you're sending them to an address. You can't prove that the address is connected to the person. You can't prove Ben didn't lose the USB key that had his wallet on it well before the transaction even took place. Did phantomcircuit send Ben money, or did phantomcircuit send money to a USB key that's in a garbage can somewhere? If someone finds that USB key and spends the money, is that proof Ben lied? Even the fact that Ben has acknowledged the transfer doesn't mean anything, depending on what exactly he acknowledged: he knows the address, so maybe his acknowledgement was just based on seeing it in blockexplorer, not actually having the wallet. Knowledge of a specific transaction isn't proof of anything, because everyone has knowledge of all transactions.
It's fairly obvious that this isn't what's going on here, because if it were, Ben would have said something to that effect, rather than taunting phantomcircuit. But
proving bitcoins were moved to a specific person is difficult to do, and in fact is something that the system was designed to prevent.