Some people might say that executing these war criminals (Nazi leaders) on the spot when they were captured would have saved time and trouble. Why was it important to bring these leaders to trial before an international tribunal?
In my view, there are at least two reasons for this.
First, it was important for the Nazi leaders to be put on a formal trial so that the world could really understand what they had done. If they had just been killed, it would have been a lot easier for people to think that the crimes of the Holocaust had not really happened. But with these men being put on trial and not really denying the facts, it became much easier to accept that these unbelievably horrible things had happened.
Second, and more importantly, it was important to try them so as to show respect for the rule of law. One of the things that was really terrible about the Nazi regime is that they did not care anything about the law. They wanted to be able to do whatever they wanted to whoever they wanted without having to follow any rules. This is one thing that made them a menace. If we had just killed their leaders because we could, we would have been acting like them. That is not the best way to repudiate their evil.