You should be punished by and in the UK. Or Brazil or wherever. Is this really such a hard concept? The murder in any case would be done on American soil which would give a U.S. court jurisdiction. Stealing from an American bank account could also be considered U.S. soil.
There are plenty of reasonable alternatives. U. S. courts punishing foreign crimes , not reasonable.
Did you read? The crime in question is extortion, not murder, and it was committed against Americans. And after he’s tried in the US, he goes right back to Peru to continue his sentence there.