Some throwaway thoughts on the replevin issue. I'm not sure that's the appropriate remedy, particularly because of the inequity to innocent good faith purchasers. Imagine this: thief scams 10 BTC a couple years ago when it was worth much less. Buys a number of trivial items for 1 BTC each. Now, someone actually sleuths out who the thief is and where the money went. It was to these ten merchants for a variety of $5 items. The 1 BTC is worth $1,000 now. To return that BTC (and the merchant probably could not return the actual BTC because that particular BTC is probably long-spent), the merchant would have to take a $995 bath. Additionally, replevin requires the return of a specific item. The merchant probably doesn't have this specific item any more. Replevin can't require you to "return" an item you don't have, or substitute an item that just happens to be like it.
Additionally, the whole idea of boycotting particular BTC (basically destroying its value forever) would be considered breaking the protocol. If there is something courts should not be encouraged to do, it is that. Additionally, just as a matter of practicality, there are current technical proposals (specifically
BIP 0032) that would render this kind of sleuthing much more difficult. One pool (Eligius run by Luke-Jr) has recently started discouraging and de-prioritizing the kind of address reuse that would make going after merchants practical.
Now, I agree that obviously, the thief is responsible to return the BTC, but I can't see a judgment ordering return in the form of a cryptocurrency. How would the court administer such a thing and decide between conflicting claims when scammer claims he shipped and judgment creditor claims he didn't? Expert testimony about BTC? Costs money. Lots of it. Probably more than it's worth.
I think the plaintiff would be entitled to a money judgment in the form of the original money value of the BTC, plus something in the form of incidental and consequential damages (in a contract action), punitive damages if the conduct was particularly to be discouraged (and some other tort was involved), and otherwise. Oh, and legal fees. Because until you're getting into the million dollar territory, prosecuting the first few cases like this is going to be an uphill slog and require explaining highly technical subjects to 70 year old judges.
An action in the nature of trover also makes some sense, i.e. a verdict for the value of the lost commodity. While arguably, BTC is identifiable rather than purely fungible, you could say that about actual cash, too. It has serial numbers. There's even a
searchable database, as an example, of the serial numbers in the D.B. Cooper heist. Money may be generally fungible, but in some cases, it can be identified as being particular stolen money.
While I understand why plaintiffs would desire to be able to go after merchants (since thieves are often judgment proof losers), especially for the current value of BTC they lost in scams which has since vastly appreciated in value, it would be grossly inequitable to the merchants, actual enforcement would be so disastrous to merchants that unless miners changed the protocol to make such a regime unenforceable (BIP 0032 would be a nice start), they would flee the market, and it would basically amount to a windfall for the plaintiffs.
