Most crimes committed by US citizens in foreign countries are in the context of their military service: War crimes. And instead of being incarcerated for those, they just complete their tour of duty and go home. With any luck there's some public outcry about their crimes, but often not even that. The US is also not party to the Rome statute (https://en.wikipedia.org/wiki/Rome_Statute), and has even threatened to personally target International Criminal Court employees if they try to prosecute US citizens.

... but I suppose you're right about more mundane, non-government-sanctioned crimes.

I do believe it. But that's not relevant, because OP is talking about an additional power.