DCI Tenet before the SSCI on The Worldwide Threat in 2000 (2 February 2000)
[nearly identical remarks also delivered to Senate Foreign Relations Committee, 21 March 2000.]

Mr. Chairman, we remain concerned that terrorist groups worldwide continue to explore how rapidly evolving and spreading technologies might enhance the lethality of their operations. Although terrorists we've preempted still appear to be relying on conventional weapons, we know that a number of these groups are seeking chemical, biological, radiological, or nuclear (CBRN) agents. We are aware of several instances in which terrorists have contemplated using these materials.

Among them is Bin Ladin, who has shown a strong interest in chemical weapons. His operatives have trained to conduct attacks with toxic chemicals or biological toxins.

HAMAS is also pursuing a capability to conduct attacks with toxic chemicals.
http://www.cia.gov/terrorism/pub_statements_cbrn.html

Other background stuff:
http://usinfo.state.gov/topical/pol/terror/99129502.htm
http://meria.idc.ac.il/journal/2001/issue4/jv5n4a3.htm
http://specials.politinfo.com/Latest_Specials/War_on_Terror/Osama_Bin_Laden___Al_Qaeda/osama_bin_laden___al_qaeda.html