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.