Here are some bin Laden quotes where he took responsibility for 9/11.
I will speak to you about the reasons behind these incidents. I will honestly tell you about the minutes in which the decision was made so that you will consider. I say to you that God knows that the idea of striking the towers never occurred to us.
But, after things had gone too far and we saw the injustice of the US-Israeli alliance against our people in Palestine and Lebanon, I started thinking of that.
The events that influenced me directly trace back to 1982 and subsequent events when the United States gave permission to the Israelis to invade Lebanon, with the aid of the sixth US fleet.
At those difficult moments, many meanings that are hard to describe went on in my mind. However, these meanings produced an overwhelming feeling to reject injustice and generated a strong determination to punish the unjust ones.
While I was looking at those destroyed towers in Lebanon, it occurred to me to punish the unjust one in a similar manner by destroying towers in the United States so that it would feel some of what we felt and to be deterred from killing our children and women...
We had agreed with the chief amir Mohammed Atta that he should accomplish all the operations within 20 minutes before Bush and his administration could take notice.
It never occurred to us that the supreme commander of the US armed forces would leave 50,000 of his citizens in the two towers to face those great horrors alone, at a time when they needed him badly.
This is because it seemed to him that being preoccupied with the little child's talk about her goat and its butting was more important than being preoccupied with the planes and their ramming into the skyscrapers.
This gave with three times the period required for carrying out the operations
Days and nights will not go by until we take revenge as we did on 11 September, and until your minds are exhausted and your lives become miserable and things turn [for the worse], which you detest.
All of the above are from Osama bin Laden's videos targeted for the western audience.
And here is another one, not from Osama himself, but still from Al Qaeda.
The Iranian government has professed on the tongue of its president Ahmadinejad that it does not believe that al Qaeda was behind 9/11 but rather, the U.S. government. So we may ask the question: why would Iran ascribe to such a ridiculous belief that stands in the face of all logic and evidence?