Complex sentence: When the door opens at the top floor, she fires several rounds of her machine gun into Gouda, killing him instantly; however, she failed to stop the assassination of Kuze at the hands of an American Empire assassin.
Split into simpler sentences: When the door opens at the top floor, she fires several rounds of her machine gun into Gouda, killing him instantly. However, she failed to stop the assassination of Kuze at the hands of an American Empire assassin.