Answer:
<h3>Act of State Doctrine.</h3>
Explanation:
According to the U.S Constitution, the Act of State Doctrine is a principle that respects the sovereignty of an independent state. It declares that sovereign states should respect the independence and integrity of other independent sovereign states.
The doctrine implies that domestic decisions of sovereign states should not be questioned by other independent states. Domestic decisions of another independent state should be respected by other independent states.
Here, since Nation A has apprehended the culprit in its country, it has the full right to decide what punishment and verdict should be given to the culprit. Through the Act of State Doctrine, it gains full immunity to handle the culprit on its own discretion. Nation B has no right to make any claims or alter the decision of Nation A.