Just out of curiosity I did some searches on stow-a-ways on ships. It is the transportation carrier's job to return the stow-a-way to their point of embarkation or their country of origin. It looks like the Japanese can hold him prisoner on board their ship until they return to his home country. There have been cases of stow-a-way's being held for over a year until the ship returns to their home country. Since the terrorist is from New Zealand they could conceivably hold him prisoner on the ship until the next time they go to New Zealand, which could be never. They also could just keep him on board until they get to the place where he boarded the ship and let him off.