Explaining 9/11 to my 9 year old

So last night when I picked up my daughters I had the radio on talk radio. They were talking about OBL and without thinking about it I left it on for about 2 minutes before realizing and changed the station. My daughters asked me about him. My oldest was born the January 2002. She never knew the world pre 9/11. She had a basic idea of what happened that day. She "knew" that he brought down the twin towers. We got home and ate dinner and after we ate she started drilling me on it. Anyone who knows my daughter knows she asks tons of questions. This is one of the things I love most about her. We sat down and I asked her what she knew about it and she knew very little. I would have liked to kept it that way but she said she wanted to know more about him and 9/11. She has a computer at home and knows how to use google. I figured I might as well be the one who tells her about it. I start explaining it as best I could, I was tearing up through most of this talk. I was afraid that I would rob her innocence by telling her of the evil in the world. She asked me some of the best questions, I was truly amazed. We talked and I never once said anything to make her lean one way or another. I wanted her to make her own judgement on it. She still didn't seem to get what happened. I showed her some clips and her eyes swelled immediately. I watched that moment it made sense to her. It was one of the hardest talks I have ever had to have.