But what good is it if you destroy one of your enemy's buildings, and he destroys one of your countries? What good is it if you kill one of his people, and he kills a thousand of yours?" asks Dr Fadl. "That, in short, is my evaluation of 9/11."
Sayyid Imam al-Sharif, who goes by the nom de guerre Dr Fadl, helped bin Laden create al-Qaeda and then led an Islamist insurgency in Egypt in the 1990s.
In a book written from inside an Egyptian prison, he has launched a frontal attack on al-Qaeda's ideology and the personal failings of bin Laden and particularly his Egyptian deputy, Ayman al-Zawahiri.
Twenty years ago, Dr Fadl became al-Qaeda's intellectual figurehead with a crucial book setting out the rationale for global jihad against the West.
Today, however, he believes the murder of innocent people is both contrary to Islam and a strategic error. "Every drop of blood that was shed or is being shed in Afghanistan and Iraq is the responsibility of bin Laden and Zawahiri and their followers," writes Dr Fadl.
He is equally unsparing about Muslims who move to the West and then take up terrorism. "If they gave you permission to enter their homes and live with them, and if they gave you security for yourself and your money, and if they gave you the opportunity to work or study, or they granted you political asylum," writes Dr Fadl, then it is "not honourable" to "betray them, through killing and destruction".
Dr Fadl was a central figure from the very outset of bin Laden's campaign. He was part of the tight circle which founded al-Qaeda in 1988 in the closing stages of the war against the Soviet occupation of Afghanistan.
By then, Dr Fadl was already the leader of Egyptian Islamic Jihad, an extremist movement which fought the Cairo regime until its defeat in the 1990s.
Source: Telegraph U.K.