In 1998, Osama Bin Laden described the acquisition of weapons of mass destruction (WMD) as "a religious duty." In 2003 a fatwa by radical Saudi cleric Nasir bin Hamd al-Fahd declared that it was legitimate to use such weapons to kill millions. This was followed in 2011 by a similar sentiment from the late al-Qa'ida ideologue Anwar al-Awlaki, permitting the use of poisons and other WMD in densely populated areas. There and many other expressions of jihadits interest in WMD have been more than mere bluster. With regard to just al-Qa'ida and its affiliates, there have been over 50 reported attempts to acquire, produce or deploy chemical biological, radiological or nuclear (CBRN) weapons in the past two decades.
Ackerman, Gary and Ryan Pereira. "Jihadists and WMD: a Re-evaluation of the Future Threat". CBRNe World .October (2014) : 27-34a