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.
But 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.
....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.
The terrorist attacks on September 11 were both immoral and counterproductive, he writes. "Ramming America has become the shortest road to fame and leadership among the Arabs and Muslims. 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."
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".