Remember the movie;'Is Paris burning?'. The German army refused to fight with the buildings of Paris as shields, and surrendered at last.
The Chinese Army of China National Party regime was different from the German army. It chose to fight with the wall and the buildings of Nanjing city as shields. (See the following map.)
Its soldiers, wearing civil clothes, opened fire from inside the private building.
Japanese soldiers could not distinguish the enemy soldiers and civilians.
Japanese soldiers had only one choice which was to kill all who wore Chinese clothing.
Japanese soldiers could distinguish women,children, and babies. But,sometimes, Japanese soldiers kill or rape them. Everybody including Japanese soldiers at the time would think that these actions are wrong, if they thought calmly.
Both of armies must apologize to the Nanjing citizens for the battle of Nanjing castle.