I assume you are basing this on the debate where Rudy snapped at him.
This about sums it up:
Giuliani vs. Ron Paul « AgapeRevolution.com
Having actually read in detail what Paul actually thinks about the situation (I will gladly provide links to his writings over the years and what research he formed his opinion from) and understanding where he is coming from, I can disagree with his logic on the matter and still see that he has never blamed the US for 9/11.