Dr. Sadao will be arrested on the charge of harboring an enemy if anyone complains against him. However,he knew that they would be arrested if they sheltered a white man in their house. The wounded man was a prisoner of war who had escaped with a bullet on his back. Since Japan was at war with America, harboring an enemy meant being a traitor to Japan.In that case he might be treated as a traitor despite his compassion for his fellow beings.