If a Danish customer takes his Danish Krones to the bank and sends them to a supplier in Germany in the form on Euros, the transaction goes like DKK → USD → EUR, so US claims jurisdiction over it and enforces its domestic laws on it:
https://www.icenews.is/2012/03/04/us-confiscates-policemans-...
And it doesn't even have to be an international transaction. Even domestic ones sometime run afoul of this limitation, as this Canadian small business owner found out:
https://www.cbc.ca/news/canada/toronto/square-canada-1.53031...
> The power of U.S. sanctions lies in the use of the U.S. dollar in most international transactions. A foreign company that sends its proceeds from trade with Iran through an international bank would likely face sanctions because part of it would be conducted in dollars. An international company with an American employee who has something to do with a transaction, no matter how inconsequential, could also run afoul of U.S. sanctions.
https://www.washingtonpost.com/world/national-security/iran-...
I'm so hazy on the details, other than that French nationals were prosecuted for alleged crimes in France because those crimes were denominated in US currency.
Edit: My memory must be wrong - there's a comment below that France will not extradite citizens
The only actual limit is if you hide in Russia or China.
And indeed, https://www.foxbusiness.com/markets/french-law-prohibits-ext... claims that French law says that France will not extradite its own citizens. And they have written that into every treaty they sign. For example http://www.mcnabbassociates.com/France%20International%20Ext... is the treaty with the USA and it includes:
Article 3(1) declares that neither State has an obligation to extradite its own nationals, but the executive authority of the United States shall have the discretion to do so. The nationality of the person sought shall be the nationality of the person at the time the offense was committed.
Article 3(2) requires a State that refuses an extradition request solely on the basis of the nationality of the person sought to submit the case to its authorities for prosecution, if so requested by the Requesting State.
It appears that you are entirely correct!
So let's say person X is wanted in the US. They get Country A to emit a warrant for them, A gets X from France, then extradites X to the US.
Also I think Germany will only extradite to EU countries.
During cold war, any kind of suspected "socialism" seemly counted as "something to do with USA" because a bunch of people were thrown out of helicopters (literally) when they couldn't be extradited.
It is a trick to avoid prosecution. When no body is found, it is hard to prove the person is dead and therefore hard to prosecute the perpetrators of the murder.