“On an al-Qaeda computer, recovered after the fall of the Taliban, [al-Qaeda second-in-command] Ayman al-Zawahiri wrote to [al-Qaeda military commander] Mohammed Atef on April 15, 1999, saying, ‘Despite their extreme danger, we only became aware of [chemical and biological weapons] when the enemy drew our attention to them by repeatedly expressing concerns that they can be produced simply with easily available materials.’ “
– Peter Bergen, The Longest War, Pages 219-220