Remembering 9-11 and difficult discussions

Eight years ago today Marcus was only 4. He was way to young to understand what had just happened to his country. Now he is 11 and full of questions.
During school today they discussed it being the anniversary of 9-11. Marcus came home talking about it. He is at that age that he wants all the details but still has a hard time grasping the reality of something so devastating.
I have spent the evening answering many questions and trying to help him understand the events of that horrible day. I took out some magazines that are eight years old. I bought Time and Newsweek right after the event. They were placed in a zip loc bag to keep them looking new. I knew this day would come and I wanted the information available for my kids as if it had just happened. We spent some time looking through them and talking about what he seen. It is now almost 8 PM and we are watching 9-11 specials on the history channel and he is still asking questions.

I had another difficult discussion with him the other day, this time about the Holocaust.
He was laughing and telling me about an episode of South Park (yes I let him watch South Park). One of the characters had said something about a stupid Jew. I calmly told him that we needed to talk, that it was time for a history lesson.
I do not even know a Jewish person but I have always had an interest in the holocaust. I really don't know why except that I think it is the worst thing that has ever happened to a group of people-ever. But how do you explain and educate a child about something unimaginable? I done it the only way I knew how to. I was honest.
I am very confident that I will never hear the word Jew in a derogatory way again.

I know I say this almost every day, but man is this parenting thing tough.