I don't see the relevance here. If you do something that's illegal in the U.S., don't go to a country that has an extradition treaty with the U.S. The only exception is war. If your country invades the U.S., and you are a normal soldier and shoot some people, if you're captured you'll be treated as a prisoner of war and released when the war is over.

If you covertly come to the U.S. and shoot some people, you'll be put on trial, convicted, and then imprisoned or executed. If the other side has someone to trade for you, you might get released. This is how spying works.