Reassessing the Threat of Bio-Terrorism

The series of anthrax-tainted letters sent through the United States mail in October 2001 which claimed five lives and infected several others, indicates that biological terrorism poses a 'clear and present danger' to national security. Although the number of anthrax exposures has been limited, a more extensive biological attack against civilians remains a real possibility.

The terrorist groups of greatest concern are those who:

  • are motivated to inflict indiscriminate mass casualties and to employ innovative and risky tactics;
  • possess the organizational structure and skills to avoid penetration by intelligence or law enforcement agencies and to prevent defection by members of the group; and
  • have the technical capabilities and know-how to acquire, produce, and deliver biological agents.
Although few terrorist organizations currently meet all three of these criteria, some characteristics of the 11 September attacks and the anthrax-contaminated letters suggest that the number of terrorist groups at the intersection of the three sets is likely to grow in the future.

Terrorist Motivation

'Traditional' terrorist organizations with defined political objectives, such as the Provisional Irish Republican Army, have not sought to employ chemical, biological or radiological weapons for indiscriminate attacks. Politically motivated groups tend to be conservative in their choice of weapons and tactics, innovating only when compelled to do so by the introduction of counter-terrorist measures. Moreover, traditional terrorist organizations calibrate their level of violence to apply political pressure on key decision-makers without alienating their political supporters at home or provoking massive repression by government authorities. Beyond having such undesired effects, indiscriminate attacks could be counterproductive by generating dissent within the group that could lead to defections and security breaches.

Recent years, however, have seen the emergence of terrorist organizations that engage in violent acts not to achieve specific political objectives but rather in pursuit of vague, inchoate goals. Examples include Islamic extremists driven by a deep resentment of Western political, military and cultural hegemony; far-right American 'patriots' and anti-government militias with a deeply paranoid, conspiratorial view of the world; and idiosyncratic cults led by charismatic but sociopathic leaders with an apocalyptic mindset.

Groups motivated by anti-Western ideology or doomsday prophecy generally do not have a political constituency in the targeted country that could exercise a moderating effect on the terrorists' level of violence. Moreover, because religious ideology often subordinates individual responsibility to divine will, groups motivated by religious extremism experience fewer moral constraints on their actions. A millenarian belief system, for example, may justify mass-casualty attacks as a means to hasten the coming of Armageddon and the 'Final Judgement'.

Most terrorist groups are conservative with respect to weapons and tactics, and the acquisition and use of biological weapons requires special expertise and entails significant risks. Conventional weapons satisfy most terrorist objectives: guns and bombs generate immediate shock and fear, produce dramatic images of death and destruction for the news media to report, and give the perpetrators an emotional catharsis. The technology of explosives is relatively accessible, easy to master, and has a high probability of success.In contrast, the rationale for resorting to biological weapons is less obvious. On the one hand, infectious agents are difficult and hazardous to handle, and their use involves considerable uncertainties. Beyond the vagaries of wind and weather, an incubation period of days or weeks would intervene before the effects of a biological attack became evident. On the other hand, the time-delay before the appearance of symptoms would make it easier for the perpetrators to escape attribution and punishment. Another 'advantage' of biological weapons is that even a small-scale attack can generate a disproportionate level of fear, as demonstrated by the far-reaching psychological and economic impact of the handful of anthrax-tainted letters.

Some terrorist organizations may also have a quasimystical fascination with poisons and disease. For example, certain white-supremacist groups in the United States inspired by Christian Identity theology have talked of unleashing biblical plagues to hasten the coming of the Apocalypse. A number of US anti-government militias are also obsessed with ricin, a potent biological toxin that the Soviet KGB employed as an assassination weapon.

Other factors associated in the past with terrorist acquisition and use of biological agents include the extreme isolation of the group from society, a tendency to escalate violent attacks over time, an interest in innovative weapons and tactics, and a willingness to take risks. Ironically, successful counter-terrorism measures to prevent conventional tactics, such as aircraft high-jacking and car bombs, may have the unintended effect of forcing terrorists into novel avenues of attack, including the use of non-conventional weapons. Innovative tactics may also be required to capture the attention of a desensitized public and news media.

Although the 11 September attacks did not involve the use of non-conventional weapons, it appears that the perpetrators would have had few qualms about employing them. Indeed, Osama bin Laden, the presumed mastermind of 11 September, has declared that it is his 'religious duty' to acquire nuclear, chemical and biological weapons for use against Americans at home and abroad. Driven by a fanatical worldview and a deep hatred of the United States, the 11 September terrorists sought to kill as many Americans as possible while striking at symbolic targets of US economic and military power. Not only did the perpetrators lack a domestic political constituency in the targeted country, but also they completely dehumanized their victims. Unlike more traditional terrorists, they showed no concern for their personal survival and, indeed, were prepared to sacrifice their own lives in carrying out the attack.

Organizational Structure

Most domestic terrorist groups that have sought to acquire non-conventional weapons in the past have been easily penetrated by law enforcement agencies or betrayed by defectors before they could carry out a successful attack. The risk of penetration is greatest in centrally organized groups with a clear hierarchical structure. In response to such setbacks, terrorist organizations have increasingly adopted a 'leaderless resistance' structure, consisting of numerous quasiindependent cells that are loosely co-ordinated so that the compromise or penetration of one or more cells will not jeopardize the entire network. In some cases, information and commands are passed through websites, which can be accessed without the need for direct communication with the top leadership.

It is remarkable that the 11 September terrorists were able to plan and carry out a massive co-ordinated attack without being detected in advance by US intelligence and law-enforcement agencies equipped with the most advanced surveillance technologies. This accomplishment may be attributable in part to the decentralised structure of the Al Qa'ida network. The terrorists were also highly skilled at covering their tracks, perhaps with the assistance of a foreign intelligence service. They made particularly effective use of covert communications techniques, such as posting images on the World Wide Web containing encrypted messages.

Technical Capabilities

Of the limited number of terrorist groups that are both motivated to employ non-conventional weapons and capable of avoiding premature arrest, an even smaller subset have the technical capability to acquire, weaponize and deliver biological agents. Terrorists seeking to carry out mass-casualty attack would have to overcome a series of challenging technical hurdles including:

  • obtaining a virulent pathogen from a natural source or a laboratory collection;
  • cultivating or manufacturing the agent in kilogram quantities;
  • weaponizing the agent by means of drying and milling it into a fine powder, and adding chemicals to enhance its stability, shelf-life in storage, and ability to be disseminated as anaerosol of microscopic particles or droplets;
  • Developing or acquiring specialized dissemination equipment capable of generating an aerosol cloud that blankets a large area and is concentrated enough to infect large numbers of people.
In the case of a contagious agent such as smallpox virus or plague bacteria, a crude delivery system would be sufficient to infect a small number of people, who would then spread the disease by secondary transmission. Even so, acquiring, producing and weaponizing a contagious agent would be technically difficult.

The Japanese doomsday cult Aum Shinrikyo, for example, failed in several attempts to carry out a mass-casualty attack with anthrax bacteria or botulinum toxin due to technical impediments. Because the cult owned a range of legitimate and illegitimate businesses and had a net worth of roughly $1 billion, it was able to recruit biologists from Japanese universities and to procure materials and production equipment from a variety of countries. Nevertheless, although Aum operatives released the causative agents of anthrax and botulism in downtown Tokyo on at least nine occasions in 1990 and 1993, the attacks produced no known casualties. The apparent cause of these failures was that the cult had unwittingly obtained non-virulent strains of anthrax and botulin bacteria.

The 11 September attack was essentially 'low-tech' in that the terrorists hijacked passenger aircraft and transformed them into flying bombs. Nevertheless, the group's tactics were innovative and complex, and the perpetrators methodically and patiently planned the attack over a period of years and even obtained specialized flight training for their operatives. This degree of preparation suggests that an equally systematic effort to acquire and deliver biological weapons might eventually overcome the technical hurdles. Surmounting these obstacles would be considerably easier if a state-sponsor or former weapons scientists were to provide the relevant materials (e.g., virulent pathogens and production equipment), along with the specialized know-how needed to weaponize and deliver disease agents effectively.

The proliferation of biological weapons to some dozen countries, most of them in the Middle East, has created new opportunities for state-sponsored bioterrorism. At the same time, the large number of unemployed and underpaid biological weapons scientists living in the former Soviet Union could provide a pool of deadly expertise. More broadly, the diffusion of the commercial pharmaceutical and biotechnology industries throughout the globe has made dual-use technologies and know-how increasingly accessible to terrorists.

The still-unknown perpetrators of the anthrax letter attacks, particularly the tainted letters sent to US Senators Tom Daschle and Patrick Leahy, were somehow able to acquire or produce 'weapons-grade' material. In particular, the anthrax spores had been dried, milled to an extremely fine powder, and treated with chemical additives to prevent clumping and render them more volatile, so they could readily infect through the lungs. Although the terrorists sent only a few grams of refined anthrax spores through the mail, the sophistication of the material was disturbing. Even if the perpetrators had the capability to produce small amounts of weaponized anthrax, however, it would not be a simple manner to scale-up the production process from grams to kilograms of dried agent and to deliver the latter effectively over a large area.


Although the 11 September attacks did not involve weapons of mass destruction (WMD) and the anthrax attacks through the mail have remained limited in scale and scope, these events have forced bio-terrorism analysts to modify their threat assessments in the harsh light of reality. Ominous developments in all three dimensions of the bio-terrorism threat - motivations, organizational structure and technical capability - suggest that the risk of a major attack is increasing. The disproportionate response to the anthrax-tainted letters also suggests that any extensive use of biological weapons, even if it failed to inflict mass casualties, would generate a higher level of public anxiety and media attention than a conventional explosion. In response to these warnings, we must reduce our future vulnerability to a biological attack, both by stockpiling relevant drugs and vaccines and by improving our disease-detection and containment capabilities.

Jonathan B. Tucker directs the Chemical and Biological Weapons Non-proliferation Program in the Washington, DC office of the Monterey Institute of International Studies.

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