If  you have the Bitcoin wallet, you can see the Bitcoin addresses. If you have the addresses, you can query the blockchain for the true value. But if you don't have the passphrase, you can't spend the bitcoins.

Probably the only reason the pirate doesn't use hidden backup wallets to move the bitcoins out of Government control to other wallets is, he is being monitored too closely for such activity. Once he can get his hands on a computer when nobody is watching him, he just might move the bitcoins to other wallets that are not under Gov control.

Of course, when Gov sees the bitcoins gone, they will jump on him. He will need an alibi. He will at least need a good form of plausible deniability.