Assessing the Threat of WMD Terrorism

Jason Pate
Gary Ackerman
August 2001

Because of a number of developments over the past decade, the threat that terrorists might resort to chemical, biological, radiological, or nuclear weapons of mass destruction (WMD) has received increased attention from U.S. policymakers, the news media, and academic analysts.


  • the proliferation of WMD-related technologies, materials, and know-how;
  • trends in terrorist incidents suggesting a growing tendency toward mass-casualty attacks for which WMD may be well suited;
  • interest in WMD expressed by Usama bin Laden, the terrorist held responsible for masterminding the August 1998 U.S. embassy bombings in Kenya and Tanzania; and
  • the March 1995 attack in the Tokyo subway by the Japanese cult Aum Shinrikyo with chemical nerve agent, demonstrating that WMD (at least chemical weapons) are within the reach of some terrorist groups.

At the same time, many analysts believe that there are significant technical hurdles to WMD acquisition and use, and that the Aum incident is the exception rather than the rule. Indeed, the lack of other major incidents of WMD terrorism in the years since the Aum attack suggests that the threat may be largely theoretical or at least is poorly understood.

In March 1995, the Japanese doomsday cult Aum Shinrikyo released sarin nerve agent in the Tokyo subway, killing 12 and injuring over a thousand. This incident, perpetrated by an apocalyptic group seeking to inflict mass casualties, demonstrated that at least some terrorist groups are capable of acquiring and using chemical weapons. One month later, in April 1995, a truck bomb destroyed the Alfred P. Murrah Federal Building in Oklahoma City, killing 168 and injuring more than 700. Perpetrated by a lone actor influenced by right-wing ideology, this unprecedented attack brought the threat of mass-casualty terrorism—albeit with conventional explosives—to the American heartland.

In the aftermath of these events, some analysts declared that a new era of terrorism had emerged, one involving a sea change in terrorist tactics and goals. With religion arguably replacing politics as the primary motivation for terrorist groups in the 1980s and 1990s, it was possible to envision terrorist groups relatively unconstrained by societal norms and seeking to inflict higher levels of violence than more “traditional” terrorist organizations. For example, bin Laden, the alleged mastermind of the August 1998 U.S. embassy bombings in Kenya and Tanzania, openly declared an interest in acquiring WMD for attacks against American targets. At the same time, the spread of dual-use technologies and materials relevant to WMD to state-sponsors of terrorism, and the lack of controls on weapons materials and know-how in the former Soviet Union, suggested that the barriers to terrorist acquisition and use of WMD had eroded.

US Counterterrorism

Since 1995, the United States has allocated enormous resources to combating WMD terrorism. Numerous government programs have been created in an effort to prevent and deter terrorism or to mitigate the effects of a major attack should it occur. These efforts have focused largely on enhancing the ability of local first responders to decontaminate and treat survivors, augmented by additional capabilities at the state and federal levels. But analysts have criticized the significant overlap and redundancy among various federal counterterrorism programs, as well as the lack of a clear strategy for integrating these diverse elements into a coherent whole.

U.S. counterterrorism efforts have also been developed in the absence of a realistic assessment of terrorist motivations and capabilities for using WMD. The Aum Shinrikyo experience, in particular, does not appear to be widely applicable. Aum certainly represents a threatening type of group, but one that is so rare that it cannot serve as a reliable indicator of things to come. Critics have also pointed out the significant technical hurdles to WMD acquisition and use. Despite Aum’s vast financial resources and scientific expertise, it was unable to perpetrate true mass-casualty attacks with either chemical or biological weapons. This observation suggests that terrorist acquisition and delivery of WMD are difficult to carry out effectively.

The threat of WMD terrorism remains poorly understood, however, suggesting the need for further empirical study based on the analysis of historical cases as well as an assessment of emerging threats. The following web-based resources offer insight into this ongoing debate.

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