Ok if you want english source: http://www.911truth.org/article.php?...70227235042773
But this was a pretext rather than the real reason for attacking Afghanistan---as illustrated by the fact that when the Bush administration had an opportunity to take bin Laden alive, it showed no interest. A week after 9/11, the Taliban said that it would hand OBL over---if the United States presented proof of his involvement in 9/11. But Bush refused to provide any such evidence, saying that there would be no negotiations or even discussion.101 Again, four weeks after the U.S. attack on Afghanistan began, a Taliban spokesman said: "We will negotiate. But . . . [w]e are not a province of the United States, to be issued orders to. We have asked for proof of Osama's involvement, but they have refused. Why?"102
(It's at point 4 alinea 3)
btw, OBL= Osama Bin Laden.

I found this in a hurry, will try to find more from BBC or CNN. But this could be rather reliable about 9/11.