Several terrorist groups have actively sought weapons of mass destruction (WMD) of one kind or another. In particular, the Japanese cult group Aum Shinrikyo, al Qaeda and its associates -- notably the Egyptian Islamic Jihad, Jemaah Islamiya and Lashkar al Tayyib -- figure most prominently among the groups that have manifested some degree of intent, experimentation, and programmatic efforts to acquire nuclear, biological and chemical weapons. To date, however, al Qaeda is the only group known to be pursuing a long-term, persistent and systematic approach to developing weapons to be used in mass casualty attacks.
Osama bin Ladin's assertion in 1998 that it was his Islamic duty to acquire weapons of mass destruction ensured that the fulfillment of this intent would become a top priority for his lieutenants in the ensuing years. In an effort to explain his thinking to his followers, and to help guide their efforts, the al Qaeda leader has offered a number of statements that provide a need and rationale for using weapons of mass destruction as a means of achieving the group's concrete and ambitious goals. Most recently, he promised in a 2007 video release to "escalate the killing and fighting against you (Americans)" -- on grounds of destroying an international conspiracy to control the world -- adding, "The capitalist system seeks to turn the entire world into a fiefdom of the major corporations under the label of globalization in order to protect democracy."
These statements should not be interpreted as empty rhetoric and idle threats: Osama bin Ladin has signaled a specific purpose for using WMD in al Qaeda's quest to destroy the global status quo, and to create conditions more conducive to the overthrow of apostate regimes throughout the Islamic world. His argument is essentially that even weapons of mass destruction -- which are outlawed under Islam -- are a justifiable means of countering US hegemony. Osama bin Ladin's morality-based argument on the nature of the struggle between militant Islamists and the US-led coalition of secular forces focuses the group's planning on the acquisition of strategic weapons that can be used in mass casualty attacks, rather than on the production of tactical, more readily available weapons such as "dirty bombs," chemical agents, crude toxins and poisons.
In this light, it is not surprising that the group's top WMD priority has been to acquire nuclear and strategic biological weapons. Considering the potential that such weapons hold in fulfilling al Qaeda's aspirations, their WMD procurement efforts have been managed at the most senior levels, under rules of strict compartmentalization from lower levels of the organization, and with central control over possible targets and timing of prospective attacks. In this sense, their approach has been "Muhammed Atta-like" -- similar to the modus operandi Khaled Sheikh Mohammed employed in making preparations for the 9/11 attacks -- as opposed to resembling the signature characterizing most terrorist attacks to which the world has become accustomed.
Al Qaeda's patient, decade-long effort to steal or construct an improvised nuclear device (IND) flows from their perception of the benefits of producing the image of a mushroom cloud rising over a US city, just as the 9/11 attacks have altered the course of history. This lofty aim helps explains why al Qaeda has consistently sought a bomb capable of producing a nuclear yield, as opposed to settling for the more expedient and realistic course of devising a "dirty bomb," or a radiological dispersal device.
Another 9/11-scale operational plot managed by the al Qaeda core leadership was the development of anthrax for use in a mass casualty attack in the United States. The sophisticated anthrax project was run personally by al Qaeda deputy chief Ayman Zawahiri, in parallel to the group's efforts to acquire a nuclear capability; anthrax was probably meant to serve as another means to achieve the same effect as using a nuclear bomb, given doubts that a nuclear option could be successfully procured. Notably, al Qaeda's efforts to acquire a nuclear and biological weapons capability were concentrated in the years preceding September 11, 2001. Based on the timing and nature of their WMD-related activity in the 1990's, al Qaeda probably anticipated using these means of mass destruction against targets in the US homeland in the intensified campaign they knew would follow the 9/11 attack. There is no indication that the fundamental objectives that lie behind their WMD intent have changed over time.
On the other hand, the pursuit of crude toxins and poisons appears to have been of little interest to the al Qaeda leadership, even though the production of such weapons is easier and thus might seem more attractive for potential use in attacks. Although experimentation and training in crude chemical agents and pathogens was standard fare in al Qaeda's camps in Afghanistan before 9/11, their use in attacks appears to have been left to the initiative of individual cells and planners outside the direct supervision of the al Qaeda core leadership. Prominent examples of small-scale chemical- and biological- related activity include Midhat al-Mursi's (aka Abu Khabab) basic training for operatives in the al Qaeda camps in Afghanistan before 9/11; the Abu Musab al Zarqawi network's plotting to use ricin and cyanide in multiple attacks planned in Europe in late 2002-early 2003; and a Bahraini terrorist cell's plot to use a crude cyanide gas device called the "mobtaker" (an Arabic word roughly meaning "invention") in an attack on the New York City subway in the same time frame.
In each of these cases, the evidence suggests that the al Qaeda senior leadership was not directly involved or apparently even aware of attack preparations until late stages of planning. Moreover, there is no evidence that the al Qaeda leadership regarded the use of crude toxins and poisons as being suitable for conducting what would amount to pin prick attacks on the United States; on the contrary, Zawahiri canceled the planned attack on the New York City subway for "something better," suggesting that a relatively easy attack utilizing tactical weapons would not achieve the goals the al Qaeda leadership had set for themselves.
So, why hasn't a terrorist WMD attack happened since 9/11?
There are many plausible explanations for why the world has not experienced an al Qaeda attack using chemical, biological, radiological or nuclear weapons, but it would be foolish to discount the possibility that such an event will occur in the future. To date, al Qaeda's WMD programs may have been disrupted. This is in fact one likely explanation, given a sustained and ferocious counterterrorist response to 9/11 that largely destroyed al Qaeda as the organization that existed before the fateful attack on the US. If so, terrorists must continue to be disrupted and denied a safe haven to reestablish the ability to launch a major strike on the US homeland, or elsewhere in the world.
Or perhaps, al Qaeda operational planners have failed to acquire the kind of weapons they seek, because they are unwilling to settle for anything other than a large scale attack in the US. It would surely be hard for al Qaeda to lower the bar they set on 9/11: what would constitute a worthy follow-up to 9/11, on their terms? What would they achieve through another attack? There are few weapons that would meet their expectations in this regard. It is extremely difficult to acquire a functioning nuclear bomb, or to steal enough weapons usable material to build a bomb. And as al Qaeda probably learned in trying to weaponize anthrax, biological pathogens may seem simple enough to produce, but such weapons are not easy to bottle up and control. To complicate matters further, an attack on the scale of 9/11 is more difficult to accomplish in an environment of heightened security and vigilance in the US.
But if Osama bin Ladin and his lieutenants had been interested in employing crude chemical, biological and radiological materials in small scale attacks, there is little doubt they could have done so by now. However, events have shown that the al Qaeda leadership does not choose weapons based on how easy they are to acquire and use, be they conventional or unconventional weapons. They choose them based on the best means of destroying the specific targets that they have in mind. Al Qaeda's reasoning thus runs counter to analytic convention that equates the ease of acquisition of chemical, biological or radiological weapons with an increasing likelihood of terrorist use -- i.e., a terrorist attack employing crude weapons is therefore more likely than an attack using a nuclear or large scale biological weapon. In fact, it is the opposite: If perpetrating a large- scale attack serves as al Qaeda's motivation for possessing WMD, not deterrence value, then the greatest threat is posed by the most effective and simple means of mass destruction, whether these means consist of nuclear, biological, or other forms of asymmetric weapons.
An examination of the 9/11 attack sheds light on al Qaeda's reasoning behind the selection of specific weapons, and how that may apply to the role WMD plays in their thinking. Al Qaeda opted to pursue a highly complex and artfully choreographed plot to strike multiple targets requiring the simultaneous hijacking of several 747 jumbo passenger aircraft, because using airplanes as weapons offered the best means of attacking the targets they intended to destroy. If conventional wisdom on assessing WMD terrorism threats had been applied to considering the likelihood of the 9/11 plot, analysts may well have concluded it never would have happened; at the time, it was simply hard to believe any terrorist group could pull off such an elaborate plot utilizing novel, unpredictable weapons that were so difficult to acquire.