Probably about 1993.
http://www.pbs.org/moyers/journal/07272007/alqaeda.html
the development of Al Qaeda, at what point in the organization’s growth do you feel it should have become a concern to United States government officials? Explain
2 answers
At least 1993. There is a really good National Geographic DVD set that goes into the background of the 1993 attack on WTC ... back before 1991.
http://channel.nationalgeographic.com/channel/episodes/war-on-america/
http://channel.nationalgeographic.com/channel/episodes/war-on-america/