Likely what makes the US special in this instance is that they did it first, and as long as other countries aren't going to make a stink about it (i.e. the US backs up its claims to some degree or the other countries don't want to question them), then it will get away with it.

Rule of law is for people. Countries operate on a mixture of laws, norms, and consensus building. If every country but one decided to raid that one country, and they had the power (as in economic and military power) to do so, what's to stop them? Not a law, which they my nature can just rewrite.

Real justification: Extraterritoriality is a thing you get to do when you're an empire.

This is exercise of extraterritorial jurisdiction, which is not the same thing as (though also not unrelated to) extraterritoriality.

And everyone gets to do it, it has nothing to do with being an empire (actual extraterritoriality beyond what is normal for, e.g., diplomats might, but this isn't that.)

  Trivial amount of money laundering

  BTC-e 

The only company within US jurisdiction that BTC-E did business with is a company called "tradehill". The amounts of money moved were small, ranging between $12.60 and $17,000. Less than $100,000 was moved overall and all of it was moved in early 2012.

The US doesn't care about tracking down the $12.60 that you laundered on 24 January 2012 like it says in the indictment. The US is just using that as an excuse to impose it's money laundering laws outside of it's jurisdiction. The indictment is a pretext for extraterritoriality. Extraterritoriality is a thing you get to do when you're an empire.

Just seems silly to try and cast the US as an "empire" here when all you're really saying is "the US is a very powerful nation".

Because no one is able to stop them.

A foreign power can have any law it wants, and no other foreign power has to respect it. You can try to sue them, but sovereign immunity, and foreign sovereign immunity, stops almost all of these attempts. The exceptions generally are human rights abuses (by the same state doing the suing...) and commercial transactions.

In this case, the USG stole from money launderers in a foreign country. So not only can people in the US not sue the USG over it (sovereign immunity), people in the Ukraine can't sue the USG over it (foreign sovereign immunity). The thieves would have the best claim, but it doesn't work out well when you claim your illegal business was stolen from. And since it's a foreign power, if the US balks, it would be covered under international law, and guess who enforces international law?

It may take some time and effort to get the property back, but there is a process.

(note: IANAL)

It looks like the man behind it was arrested while holidaying in Greece - a US ally.

At some point, someone will want to do something in the real world with this money, and the government can step in there.