Assessing the Threat of Mass-Casualty Bioterrorism

Assessing the Threat of Mass-Casualty Bioterrorism

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Gary Ackerman

Senior Research Associate, The James Martin Center for Nonproliferation Studies

Jason Pate

Deputy Director, Chemical and Biological Weapons, Nonproliferation Program


The September 11, 2001 terrorist attacks that destroyed the World Trade Center in New York, damaged the Pentagon in Washington, D.C., and caused a plane crash in Pennsylvania conclusively demonstrated that mass-casualty terrorism has reached the United States. The subsequent series of anthrax letters showed that biological terrorism, which had been largely a theoretical possibility, is a reality. These two developments, as well as several revelations regarding the al-Qai'da terrorist network's interest in weapons of mass destruction, have placed the threat of terrorists causing mass casualties using biological agents squarely before policymakers and an anxious public.

Although the anthrax letters did not appear to have been designed to cause mass casualties, there is now great concern that these or similar perpetrators might employ higher technology delivery systems and affect larger numbers of people in future attacks.

The September 11 attacks and the subsequent anthrax letters, combined with evidence of al-Qai'da's interest in toxic agents, have focused renewed attention on the possibility of terrorism involving chemical, biological, radiological, or nuclear weapons, commonly called weapons of mass destruction (WMD). WMD terrorism is not a new phenomenon: in March 1995, the Japanese doomsday cult Aum Shinrikyo released sarin nerve agent in the Tokyo subway, killing 12 and injuring over 1,000. 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. Mass-casualty terrorism is also not new to the United States. 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 ideological motivation for terrorist groups, it was possible to envision terrorist groups, relatively unconstrained by societal norms, seeking to perpetrate more extreme acts of violence than more "traditional" terrorist organizations. For example, Usama bin Laden, the alleged mastermind of the September 11 attacks, the 1999 bombing of the USS Cole in Yemen, and the 1998 near-simultaneous bombings of the U.S. embassies in Kenya and Tanzania, openly declared an interest in acquiring WMD for attacks against American targets; more recently, alleged members of his organization have been apprehended with dangerous poisons. At the same time, the spread of dual-use technologies and WMD-relevant materials to state-sponsors of terrorism and the lack of controls on weapons materials and know-how in the former Soviet Union have raised serious concerns about the increasing threat of terrorists acquiring and using WMD. This is especially relevant in the context of increasing tensions and possible conflict between the United States and countries that have developed WMD and have supported terrorist groups in the past, such as Iraq and North Korea.

The Anthrax Attacks and Bioterrorism

The anthrax letters of 2001 were an entirely new phenomenon. They moved the threat of bioterrorism, which had previously been mostly theoretical, closer to reality. Despite hundreds of anthrax hoaxes in the few years prior to October 2001, the anthrax letters represented the first time that actual, virulent anthrax spores were sent through the mail. The attacks were scattered, isolated incidents targeted at prominent media and political figures, but also resulted in a number of people, notably postal workers and congressional staff, suffering from collateral exposure. One of the most significant aspects is that, thus far, the perpetrator remains at-large.

There have been conflicting reports from various government agencies regarding the quality of the anthrax used in the attacks. It may have been highly sophisticated: milled to a fine powder and treated with chemical additives to keep the spores from clumping and becoming weighed down by humidity, so that they aerosolize more readily.

The Perpetrators

The fact that the anthrax may have been milled to a fine powder and mixed with chemicals-techniques involving specialized military knowledge unlikely to be available to laboratory microbiologists-suggests that the perpetrator(s) may have been involved at one point in time with the biological weapons program of a state-perhaps even a scientist who worked on the former U.S. biological weapons program. Although the chemical additives are readily available, the critical skill is knowing which additives to use, and how and when to use them.

These findings are consistent with a number of hypotheses: the perpetrators were aided by a foreign state, were assisted by scientists who once worked in a state-level bioweapons program, or purchased the anthrax on the international black market. The FBI has released only a vague profile of the perpetrator(s), as most probably male, with a scientific background and an intimate knowledge of Trenton, New Jersey.

The fact that the same strain of anthrax appears to have been used in the letter attacks directed against individuals in Florida, New York, and Washington, D.C. also suggests that this is a coordinated effort by a single individual (i.e., a biological Unabomber), a small domestic group, or a large network such as al-Qai'da. Still, the identity of the perpetrator or perpetrators remains unclear. Some evidence, such as the quality of the anthrax, points to an international source, but other evidence points in the direction of domestic terrorists.

Mass-Casualty Terrorism

According to terrorism scholar Bruce Hoffman, until September 11, 2001, fewer than 1,000 Americans had been killed in terrorist attacks in the United States or abroad since 1968. The quantum leap in casualties-with more than 3,000 dead-is particularly alarming in terms of terrorist motivations. Terrorist trends have suggested an increase in casualties per incident, and the September 11 attacks appear to conform to this pattern. However, the anthrax incidents have been small in scale, with the apparent intent of frightening rather than killing large numbers of people.

It is possible that the perpetrators of the anthrax attacks had only a limited amount of powdered anthrax spores-enough to deliver in small amounts through the mail, but not enough to disseminate through the air as an aerosol cloud that could infect large numbers of people. They may also not have been motivated to inflict mass casualties, even if they could. Critics have also pointed out the significant technical hurdles to the use of chemical or biological weapons to cause massive numbers of casualties. Despite Aum Shinrikyo's vast financial resources and scientific expertise, it was unable to perpetrate mass-casualty attacks with either chemical or biological weapons. In any case, large numbers of casualties can be caused by terrorists without resorting to WMD. The September 11 terrorists did not require advanced weaponry to cause mass casualties and mass destruction. They used a low-technology operation and returned to decades-old terrorist tactics-hijacking planes-to achieve their goals.

One thing that the 2001 anthrax attacks made abundantly clear is that public health is a key component of U.S. national security. The anthrax attacks revealed serious gaps in the public health system, particularly at the state and local levels. Fortunately, alert physicians diagnosed the early cases correctly. One would hope that the attacks served as a lesson to public health officials by putting them on guard for the possibility of a covert bioterrorist attack, thus lessening the impact of any future attack. Yet many other doctors and health departments in other cities and towns around the country are not prepared to recognize or contain a bioterrorist attack. These gaps must be remedied immediately if the country is to be prepared for more serious threats. Indeed, improving the public health infrastructure will help address the threat posed by bioterrorism as well as the arguably much greater threat from emerging infectious diseases.

The silver lining of the current dark cloud is that there is a window of opportunity to improve our preparedness for a larger-scale biological attack. It is important, however, to address these vulnerabilities in a systematic and determined way, rather than continuing to ride the sine wave of alarmism and complacency that has plagued earlier efforts to improve domestic preparedness.

U.S. policymakers must also be prepared for an entirely different type of attack. If terrorists have access to a significant manufacturing capability, the United States must be prepared for the possibility of an escalation from targeted attacks to mass-casualty attacks with powdered anthrax or some other agent. The most ominous, but not the most likely, threat would involve the deliberate release of a contagious agent, such as pneumonic plague or smallpox. The health system would then have to detect and contain the outbreak before it spread widely.

Concerns about mass-casualty bioterrorism have again been raised in connection with Usama bin Laden's al-Qai'da group. Uncorroborated testimony in a high-profile Egyptian trial in 1999 indicated that al-Qai'da had acquired dangerous biological agents such as the anthrax bacterium, the Ebola virus, salmonella, and botulinum toxin, while other reports mentioned plague and ricin. al-Qai'da's purported research efforts were focused on weaponizing anthrax, and U.S. forces discovered a partially built biological weapons lab near Kandahar that was designed to produce anthrax even though no actual agents were found. There is still no conclusive evidence that al-Qai'da succeeded in weaponizing any of these agents. However, in January 2003, traces of the toxin ricin was found in an apartment in London used by a group of men potentially linked to al-Qai'da.

At the same time, there are fears that potential conflict with Iraq could result in Saddam Hussein becoming desperate enough to hand over some of his suspected remaining biological weapons arsenal to terrorists in the hopes that they will use the weapons against the United States.

Preparations and Consequence Management for Bioterrorism

Preventing mass-casualty terrorism with WMD agents and, if prevention fails, managing the consequences of an attack, is an enormously demanding task. 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. These efforts have focused 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. The events of September 11 and the subsequent anthrax attacks have also contributed to these efforts. President Bush, together with Congress, created a new government agency, the Department of Homeland Security, in an effort to ensure greater coordination in response and intelligence collaboration.

Planning domestic preparedness requires coordinating not only some 40 federal agencies, but also a large number of state and local agencies, as well as important elements of the private sector. The creation of the Department of Homeland Security is a useful first step, but the department's head, Tom Ridge, will have to overcome budgetary bottlenecks and chronic turf battles among rival federal bureaucracies.

In order to be prepared for a range of contingencies, the first line of defense is to train doctors to recognize the effects of a variety of biological threat agents, and to establish clear channels of communication among primary care physicians and local health departments, as well as among local, state, and federal public health officials. These various levels must be integrated by e-mail and other communications networks into a seamless web. Diagnostic laboratories around the country also need to have the appropriate tests to identify exotic disease agents such as anthrax in patient specimens. Finally, national distribution mechanisms for drugs and vaccines must be developed so that an outbreak of disease can be contained rapidly. The private sector, such as the U.S. chemical industry, transportation, energy, telecommunications infrastructure, and food companies, will also need to spend more to ensure the safety and security of their products and services.

The optimal approach to WMD terrorism is prevention, rather than consequence mitigation. U.S. counterterrorism efforts designed to address this threat have generally been developed in the absence of a realistic assessment of terrorist motivations and technical capabilities for using WMD. To the extent possible, intelligence collection and analysis capabilities must be strengthened to assess the ability of terrorists to acquire, produce, and deliver biological and chemical agents. Improved capabilities are needed to distinguish between natural and deliberate outbreaks of disease. These new challenges will require the intelligence community to improve its depth of expertise in microbiology, chemistry, and epidemiology.


The threat of bioterrorism has not receded since the anthrax attacks of 2001, especially since the perpetrator or perpetrators of those attacks remains unidentified. Recent reports concerning al-Qai'da's efforts to develop biological weapons and the possibility of conflict in Iraq have only increased fears. Despite some empirically based studies and the rich literature on terrorism and WMD issues, the threat of escalation to WMD terrorism remains poorly understood. Continued threat assessments, evaluations and re-evaluations of current policies, and heightened vigilance on the part of intelligence agencies will be essential to prepare for the future. See the following "Relevant Resources" section for web-based resources that offer some insights into these issues.


Articles and Reports

  • Richard Pilch, M.D., "Smallpox: Threat, Vaccine, and U.S. Policy," Center for Nonproliferation Studies, January 2003,
  • Michael Barletta, "Biosecurity Measures for Preventing Bioterrorism," Center for Nonproliferation Studies, November 27, 2002,
  • Kristin Thompson, "Legislative Response to Potential Bioterrorist Threat," Center for Nonproliferation Studies, July 12, 2002,
  • Laura Snyder and Jason Pate, "Tracking Anthrax Hoaxes and Attacks," Center for Nonproliferation Studies, May 20, 2002,
  • Gary A. Ackerman and Jeffrey M. Bale, "Al-Qaida and Weapons of Mass Destruction," Center for Nonproliferation Studies, December 31, 2002,
  • Barbara Hatch Rosenberg, "Analysis of the Anthrax Attacks," Federation of American Scientists, September 22, 2002,
  • Amy Smithson and Leslie-Anne Levy, "Ataxia: The Chemical and Biological Terrorism Threat and the US Response," Stimson Center Report No. 35 (October 2000),
  • Jean Pascal Zanders, "Assessing the Risks of Chemical and Biological Weapons Proliferation to Terrorists" The Nonproliferation Review 6 (Fall 1999), pp. 17-34,
  • Ehud Sprinzak, "The Great Superterrorism Scare," Foreign Policy (Fall 1998), pp. 110-124,
  • Bruce Hoffman, "Terrorism and WMD: Some Preliminary Hypotheses," The Nonproliferation Review 4 (Spring-Summer 1997), pp. 45-53,

Chronologies and Charts

  • 2000 WMD Terrorism Chronology: Incidents Involving Sub-National Actors and Chemical, Biological, Radiological, or Nuclear Materials,
  • Chronology of Aum Shinrikyo's CBW Activities, Center for Nonproliferation Studies (March 2001),
  • Resource Page for Agricultural Terrorism, Center for Nonproliferation Studies (September 2000),
  • Organizational Chart of U.S. Terrorism Response, Center for Nonproliferation Studies (July 2000),

Op-Eds and Opinion Pieces

  • Jason Pate, "Better Plan Needed to Curb Epidemics," Newsday, November 29, 2000, p. A43,
  • Jonathan B. Tucker and Amy Sands, "An Unlikely Threat," The Bulletin of the Atomic Scientists Vol. 55 (July/August 1999), pp. 46-52,
  • Ehud Sprinzak, "What Is The Real Threat, WMD or Car Bombs? Terrorism, Real and Imagined," Washington Post, August 19, 1998, p. A21.
  • Jessica Stern, "Taking the Terror Out of Bioterrorism," New York Times, April 8, 1998,

Official Documents and Reports

  • U.S. General Accounting Office, Combating Terrorism: Comments on Counterterrorism Leadership and National Strategy, testimony document no. [GAO-01-556T], March 27, 2001,
  • Assessing the Threat, First Annual Report to the President and the Congress, Advisory Panel to Assess Domestic Response Capabilities for Terrorism Involving Weapons of Mass Destruction, (Gilmore Commission Report), December 15, 1999,
  • Combating Terrorism: Need for Comprehensive Threat and Risk Assessments of Chemical and Biological Attacks, report to U.S. General Accounting Office [NSIAD-99-163] (September 1999),

Congressional Testimony

  • U.S. House Committee on Government Reform, Subcommittee on National Security, Veterans Affairs and International Relations, Combating Terrorism: Federal Response to a Biological Weapons Attack, July 23, 2001,
  • U.S. House Committee on Government Reform, Subcommittee on National Security, Veterans Affairs, and International Relations and the Committee on Transportation and Infrastructure, Subcommittee on Economic Development, Public Buildings and Emergency Management, Testimony of James Clapper, Jr., April 24, 2001,
  • U.S. House Committee on Government Reform, Transportation and Infrastructure, The Honorable Wayne T. Gilchrest Joint Hearing Testimony, April 24, 2001,
  • U.S. House Committee on Government Reform, Subcommittee on National Security, Veterans Affairs and International Relations, Combating Terrorism: In Search of a National Strategy, March 27, 2001,
  • U.S. House Subcommittee on National Security, Veteran Affairs, and International Relations, Combating Terrorism: Assessing Threats, Risk Management, and Establishing Priorities by John Parachini, July 26, 2000,
  • U.S. General Accounting Office, Subcommittee on Oversight, Investigations, and Emergency Management, Committee on Transportation and Infrastructure, Combating Terrorism: Issues in Managing Counterterrorist Programs by Norman J. Rabkin, April 6, 2000,
  • U.S. House Subcommittee on National Security, Veteran Affairs, and International Relations, Assessing the Threat of Bioterrorism by Ray Zilinskas, October 20, 1999,

Court Documents

  • Center for Nonproliferation Studies, WMD Terrorism and Usama bin Laden, March 7, 2001,

Books and Print Material

  • Jonathan B. Tucker, ed., Toxic Terror: Assessing Terrorist Use of Chemical and Biological Weapons (Cambridge: MIT Press, 2000).
  • Jessica Stern, The Ultimate Terrorists (Cambridge: Harvard University Press, 2000).
  • National Research Council, Chemical and Biological Terrorism: Research and Development to Improve Civilian Medical Response (National Research Council, National Academy Press, 2000).
  • Bruce Hoffman, Inside Terrorism (New York: Columbia University Press, 1999).
  • Ian O. Lesser, et al., Countering the New Terrorism (Santa Monica: RAND Corporation, 1999).
  • Simon Reeve, The New Jackals: Ramzi Yousef, Osama bin Laden and the Future of Terrorism, (Boston: Northeastern University Press, 1999).
  • Richard A. Falkenrath, et al., America's Achilles' Heel: Nuclear, Biological, and Chemical Terrorism and Covert Attack (Cambridge: MIT Press, 1998).

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