Answer:
Rainsford killing Zaroff was justifies because he did it for self-defense. Rainsford did not know if Zaroff would keep his promise of letting him go, so he killed him just to be safe. Some people may say that it was not justified and he could have just left since he won the game. However, if he did not kill Zaroff, many other men would be victim to his dangerous game. Zaroff had already killed many people and he would be dangerous if he was kept alive. Rainsford not only acted in self defense for himself but also for others. Therefore he was justified in killing zaroff