I just want to point out how stupid it is to even consider involving any government agency.
They will respond with one answer: "Have the victim contact us"
So unless you think Satoshi is going to magically appear and start being buddy buddy with a spook, best just rely on vigilantes ;-)
Also, has no one considered how utterly confusing this is; Someone demands to be paid *to* dox; instead of *not* to dox?
The whole thing is just... backwards.
P.S. if the hacker had anything useful, they wouldn't have posted a stupid invoice for mining equipment; that was obviously not satoshi.
The FEDs can still investigate, if they choose to. It's a crime by one person in the US using the internet, which can make it a cross State and international crime of interest to them.
http://www.federalcharges.com/blackmail-laws-charges/