Terrorist Motivations for Chemical and Biological Weapons Use: Placing the Threat in Context
Report for Congress
Terrorist Motivations for
Chemical and Biological Weapons Use:
Placing the Threat in Context
March 28, 2003
Audrey Kurth Cronin
Specialist in Terrorism
Foreign Affairs, Defense, and Trade Division
Congressional Research Service ˜ The Library of Congress
Terrorist Motivations for
Chemical and Biological Weapons Use:
Placing the Threat in Context
There is widespread belief that the likelihood of terrorist use of chemical and
biological weapons (CBW) is increasing, in part as a result of publicized new
evidence of terrorist interest and capabilities, as well as the political fall-out from the
war in Iraq. This is a serious present concern that deserves examination in the
broader framework provided by the patterns, motivations and historical context for
the current terrorist threat. Although it can have a powerful psychological impact,
past CBW use by terrorists has been rare and has not caused a large number of
casualties, especially compared to other weapons. Terrorist attacks are deliberately
designed to surprise, so no trend analysis will ever perfectly predict them, especially
in the contemporary international climate. This report presents the arguments for and
against future nonstate terrorist acquisition and/or use of CBW weapons against the
United States, as well as a brief discussion of issues for congress concerning how
best to counter the threat. It will not be updated.
Possible Reasons for Increased Terrorist Use............................2
Possible Reasons Against Terrorist Use................................6
Issues for Congress................................................7
Terrorist Motivations for
Chemical and Biological Weapons Use:
Placing the Threat in Context
Current popular attention being paid to the threat of chemical and biological
weapons (CBW) use by terrorists may give the impression that this is a new
phenomenon, but it is not. Most chemical and biological weapons themselves have
a long history: the first chemical weapons were used in ancient Greece; biological
weapons have been used in a wartime context since at least the Middle Ages.1
Employed extensively in the first World War, notably in the use of mustard gas,
chemical weapons have evolved very little in their technology since the mid-
twentieth century. Although recent technological advances in biological weapons
have been made, the vaccines and treatments available to deal with some of them
have also advanced. Historically, most terrorist groups have avoided using CBW, in
part because they do not want to alienate their own constituencies, and in part
because they have not had the technical expertise to turn them into effective
weapons.2 Those CBW attacks that have occurred represent a small proportion of the
total number of international terrorist incidents.3 CBW weapons have rarely been
used by subnational groups.
But there is growing concern that past patterns of use could be about to change.
Many experts worry about the increasing availability of CBW in the last decade or
so, combined with the serious psychological impact that their use would have. This
concern was heightened after 1995, when the Japanese terrorist organization Aum
Shinrikyo used the chemical nerve agent sarin on the Tokyo subway, killing 12
1 “Chronology of State Use and Biological and Chemical Weapons Control,” Center for
Nonproliferation Studies, Monterey Institute of International Studies, accessed at
2 For more information about technical aspects of the threat, see CRS Report RL31669,
Terrorism: Background on Chemical, Biological, and Toxin Weapons and Options for
Lessening Their Impact, by Dana Shea., and CRS Report RL31332, Weapons of Mass
Destruction: The Terrorist Threat, by Steve Bowman.
3 For example, the U.S. State Department lists 348 international terrorist attacks for 2001,
whereas the Center for Nonproliferation Studies lists only 25 CBW attacks. Even
accounting for differences in how incidents are counted, there is a large magnitude of
difference. U.S. Department of State, Patterns of Global Terrorism, Office of the
Coordinator for Counterterrorism, May 2002, p. 171; and Adam Dolnik and Jason Pate,
“2001 WMD Terrorism Chronology,”CNS Reports, Monterey Institute of International
Affairs, accessed at [http://cns.miis.edu/pubs/reports/cbrn2k1.htm].
people and injuring up to 6,000. The group’s efforts, which fell far short of its goals,
attracted widespread attention and helped increase focus on the so-called weapons
of mass destruction (WMD) terrorist threat.
While there is considerable information about state acquisition and/or use of
CBW, evidence regarding nonstate acquisition and/or use is contradictory and often
sketchy.4 Although hard evidence is limited, a sampling of terrorist groups or
individuals that are reported to have shown an interest in or used chem-bio agents
(usually in very limited ways) includes the PKK (Kurdistan Worker’s Party), believed
to have weaponized the nerve gas sarin; HAMAS (Islamic Resistance Movement),
which has reportedly coated shrapnel with poisons and pesticides; numerous U.S.
domestic individuals and groups without foreign connections (including the
Minnesota Patriots Council, the so-called “Alphabet Bomber,” R.I.S.E., Larry Wayne
Harris, and others) who have used or intended to use ricin, plague, anthrax, hydrogen
cyanide, sarin, and other agents; and of course Al Qaeda and its associated groups.5
But the efforts of Aum Shinrikyo represented a watershed, with its bizarre and
seemingly irrational agenda, its systematic pursuit of technical competency, and its
repeated attempts to kill a large number of Japanese civilians. Even with its multiple
technical failures, Aum Shinrikyo led to heightened anxiety about the attractiveness
and feasibility of future mass casualty terrorist use of CBW.
Still, numerical trends for CBW attacks have not increased. According to the
Monterey Institute of International Studies’ terrorism chronology, between 2000 and
2001 (the last year for which published data are available), the number of hoaxes
went up (from 25 to 603) but the number of CBW incidents actually decreased (from
48 to 25).6 Thus it would appear that the fall 2001 anthrax attacks in the United
States resulted in numerous copy-cat hoaxes, but they did not reflect an overall
increase in bioterrorism events. However, terrorism experts continue to worry about
the use of chemical and biological agents.
Possible Reasons for Increased Terrorist Use
The reasons for increased potential use can be grouped into four major
categories: the growth of militant religious groups with political agendas as a
percentage of all terrorist groups, the increasing global availability of CBW
information and stockpiles, the internationalization of the threat of terrorism, and the
clear evidence of terrorist interest and capabilities.
4 Indeed, some of the most-often cited examples of terrorist use of chem-bio agents have
proven to be overblown or lacking evidence. See Jonathan B. Tucker, editor, Toxic Terror:
Assessing Terrorist Use of Chemical and Biological Weapons (Cambridge, Mass.: MIT
Press, 2000), especially chapters 3, 6, and 7.
5 Amy Sands, “Deconstructing the Chem-Bio Threat: Testimony for the Senate Foreign
Relations Committee,” March 19, 2002, accessed at
[http://cns.miis.edu/pubs/reports/asands.htm], p. 6; Patterns of Global Terrorism 2001; and
Tucker, Toxic Terror. This list is illustrative, not comprehensive.
6 Dolnik and Pate, “2001 WMD Terrorism Chronology.”
First, there has been a sharp increase in militant religious groups internationally
as a percentage of all terrorist groups. Over the last years of the twentieth century,
such groups went from being just over three percent of all identified terrorist groups
in 1980 to forty-three percent by 1995.7 Militant religious terrorists, experts note,
may label their victims as heretics or infidels and thus unfit to live. The incentives
for such groups to kill large numbers of people may thus be unconstrained by the
scruples of earthly constituencies.
In combination with this worrisome development, the lethality per terrorist
attack went up over the course of the past decade. While there were fewer attacks
overall in the 1990s, the number of people killed and maimed per attack increased.
This confirmed the fear of many experts that terrorism based on extreme religious
beliefs, in association with other developments discussed below, might be even more
dangerous than were the left wing, right wing, and ethnonationalist/separatist groups
that predominated in earlier years.8 A larger proportion of the attacks that did occur
were executed by persons with religion-based animus. The tragedies of September
Second, there is a growing concern about the increasing availability of
information and resources for the building of weapons by subnational groups that in
former years had been feasible only with the resources of a state. Like the rest of the
world, terrorist groups have access to the vast amount of technical data disseminated
through the Internet. More and more information that might previously have been
difficult to collect is becoming easily accessible. Among the groups that have
reportedly demonstrated interest in acquiring unconventional weapons (besides Al
Qaeda) are the PLO, the Red Army Faction, Hezbollah, the Kurdistan Workers’
Party, German neo-Nazis, and the Chechens.9 At the same time, the breakup of the
Soviet Union increased potential access to a vast, highly advanced arsenal of not only
nuclear but also chemical and biological weapons and expertise. The combination
of greater movement of people, knowledge and products across borders in a
globalized world, and greater availability of materials and expertise in the post-Soviet
era, have together led to a potentially serious erosion in state control over chemical
and biological weapons (or their ingredients).10
7 In 1980 there were 2 out of 64, and in 1995 there were 25 out of 58 religious groups listed
in the RAND-St. Andrews University Chronology of International Terrorism. See Bruce
Hoffman, Inside Terrorism, (New York: Colombia University Press, 1998) pp. 90-91; and
Nadine Gurr and Benjamin Cole, The New Face of Terrorism: Threats from Weapons of
Mass Destruction (London: I.B. Tauris, 2000), pp. 28-29. Admittedly, some of that increase
may be accounted for by changes in how groups are categorized.
8 These figures are derived from an examination of annual data from Patterns of Global
Terrorism. See Audrey Kurth Cronin, “Behind the Curve: Globalization and International
Terrorism,” International Security, Vol. 27, No. 3 (Winter 2002/03), p. 42-43.
9 Richard A. Falkenrath, Robert D. Newman, and Bradley A. Thayer, America’s Achilles’
Heel: Nuclear, Biological, and Chemical Terrorism and Covert Attack (Cambridge, Mass.:
MIT Press, 1998), pp. 31-46.
10 Another factor is the general increase in off-the-shelf technology that is dual-use in nature.
See CRS Report RS21422, Dual-Use Biological Equipment: Difficulties in Domestic
Third, the nature of international terrorism has evolved in dangerous ways in
recent years. Although many traditional groups carry on in their struggles, the growth
of religiously-oriented groups has led to an increased commonality of interests
between populations in disparate geographical areas. In part in reaction to American
global policies and cultural as well as political global reach, groups are developing
ties across formerly divisive ideological, ethnic, and national lines. The area of
potential recruits is thus broader than it might have been for a traditional
ethnonationalist/separatist group supported only by its local constituency, for
example. Also, this internationalization of the threat has often led to a greater
distance between groups and targets. The result is not only a removal of moral
constraints but also political constraints, with less worry about potentially sullying
a homeland or killing potential constituents. Thus, the internationalization of
terrorism may unfortunately imply an increase in just the sorts of incentives that lead
groups to consider unconventional weapons.
Fourth, and perhaps most important, there are clear indications of interest in
CBW on the part of contemporary terrorist groups, as well as some evidence of actual
capabilities. With a long-standing expressed desire to acquire them and a
demonstrated willingness to kill Americans, Al Qaeda (and its associates) is the
group that most worries U.S. experts. Osama bin Laden has reportedly pursued the
development of chemical and biological weapons since the early 1990s.11 In 1998,
he spoke of acquiring weapons of mass destruction being a “religious duty,” and the
eleventh volume of Al Qaeda’s 5,000-page “Encyclopedia of Jihad” is devoted to
explaining how to construct CBW.12
There are many substantiated examples in the open press of efforts by Al Qaeda
and its allies to develop these weapons. During operations in Afghanistan, coalition
forces found trace amounts of ricin and anthrax at five or six sites, as well as
evidence of an interest in plague, cyanide, and botulinum toxin.13 In December
2001, CNN obtained a cache of 64 Al Qaeda video tapes containing gruesome
evidence of experiments using an apparent nerve gas against dogs.14 Further afield,
in 2002 a reported plot by nine Moroccans to use a cyanide compound to poison the
Regulation, by Dana Shea.
11 The Central Intelligence Agency, Unclassified Report to Congress on the Acquisition of
Technology Relating to Weapons of Mass Destruction and Advanced Conventional
Munitions, 1 January Through 30 June 2001, accessed at
[http://www.cia.gov/cia/publications/bian/bian_jan_2002.htm], on March 11, 2003.
12 Kimberly McCloud, Gary A. Ackerman, and Jeffrey M. Bale, “Chart: Al-Qa’ida’s WMD
Activities,” Center for Nonproliferation Studies, Monterey Institute of International Studies,
accessed at [http://cns.miis.edu/pubs/other/sjm_cht.htm], on March 6, 2003.
“Al Qaeda: Anthrax Found in Al Qaeda home,” Global Security Newswire, 10 December
2001; Judith Miller, “Labs Suggest Qaeda Planned to Build Arms, Officials Say,” New York
Times, September 14, 2002; cited Ibid.
14 Nic Robertson, “Tapes shed new light on bin Laden’s network,” CNN.com/U.S. August
19, 2002; accessed at [http://www.cnn.com/2002/US/08/18/terror.tape.main/index.html] on
March 26, 2003.
water supply of the U.S. Embassy in Rome was disrupted; several of the men
involved had ties to Al Qaeda.15 In January 2003, a reported plot by six Algerians to
use ricin was uncovered in a London apartment. One of the six arrested had attended
Al Qaeda training camps, whereas the others had received training in Chechnya and
the Pankisi Gorge region of Georgia.16 Most recently, evidence seized in March 2003
with the arrest of operations chief Khalid Shaikh Mohammed demonstrated
surprising technical sophistication, with production timetables and manufacturing
specifications for bio-chemical agents, especially weaponized anthrax.17 In addition
to these highly publicized examples, there are many other press reports of varying
It is hard to know with confidence what the logic of this apparently growing
interest in CBW is. If high casualties are the intended end, these agents are not the
most effective means: chem-bio agents are generally more useful for increasing
anxiety and panic than causing high numbers of casualties. Projections of tens of
thousands of casualties are theoretically possible,18 but many such estimates are
worst-case scenarios likely to occur in hard-to-achieve circumstances, with ideal
weather conditions, temperature controls, dispersion rates, concentrations of agent,
and so on.19 Still, terrorism is a psychological weapon, intended for political effect.
The goal might instead be to cause economic damage, or to show strength and
increase political support or leverage, or to copy other terrorist groups, or to emulate
the technological capabilities of states–or some combination of these. While this is
a fine line to draw, there is a danger that Western governments might overstate and
hype the threat, leading to some of the same outcomes by heightening anxieties.
There are a large number of practical obstacles to terrorists using these weapons, and
these will be discussed next.
15 Eric Coddy, Matthew Osborne, and Kimberly McCloud,”Chemical Terrorist Plot in
Rome?” Research Story of the Week, Center for Nonproliferation Studies, Monterey
Institute of International Studies, accessed at [http://cns.miis.edu/pubs/week/020311.htm],
on March 19, 2003.
16 Jeffrey M. Bale, Anjali Bhattacharjee, Eric Croddy, Richard Pilch, “Ricin Found in
London: An al-Qa`ida connection?” CNS Reports, Center for Nonproliferation Studies,
Monterey Institute of International Studies, accessed at
[http://cns.miis.edu/pubs/reports/ricin.htm], on March 6, 2003.
17 Barton Gellman, “Al Qaeda Near Biological, Chemical Arms Production,” The
Washington Post, March 23, 2003, pp. A1 and A10.
18 The most well known and oft-cited example is Secretary of Defense William Cohen’s
1997 interview with ABC News, where he held up a five-pound bag of sugar and speculated
that this amount of anthrax spores could wipe out Washington, D.C. “Interview with
William Cohen,” ABC This Week, November 16, 1997, Transcript #97111604-j12,
transcribed by the Federal Document Clearing House, Inc., (New York, New York:
American Broadcasting Co., 1997).
19 See Amy E. Smithson and Leslie-Anne Levy, “Grounding the Threat in Reality,” Chapter
2 of Ataxia: The Chemical and Biological Terrorism Threat and the US Response, Report
No. 35, Henry L. Stimson Center, Washington, D.C., 1999, pp. 11-69; accessed at
[ h t t p : / / www.st i mson.or g/ cbw/ pubs.cf m?i d=12] .
Possible Reasons Against Terrorist Use
There are at least four reasons why terrorist groups like Al Qaeda might avoid
using chem-bio agents in attacks against the United States and its interests. First and
most important, the technical difficulties in carrying out such attacks continue to be
significant. Aum Shinrikyo is a good example of a group that had unusually
favorable circumstances for producing chemical and biological weapons, including
money, facilities, time and expertise, yet they were unable to do so effectively. Some
experts argue that Aum Shinrikyo’s experience, which included problems ranging
from obtaining biological seed cultures to effectively disseminating them to chemical
leaks and accidents, is as easily a warning of the technical challenges involved as it20
is an example for future groups. For most nonstate actors, difficulties with
acquiring materials, maintaining them, transforming them into weapons, and
disseminating them effectively are numerous. While many technical advances have
occurred in recent years, arguably reducing the barriers somewhat, there are still21
considerable obstacles to terrorist development of chemical and biological weapons.
Second, as mentioned above, there are far easier and potentially more
“effective” (at least in terms of casualty numbers) alternatives to chemical and
biological weapons. On the rare occasions when they have been used, CBW have not
resulted in large death tolls, especially compared to conventional weapons such as22
truck bombs and individual explosive devices. It is worth bearing in mind that the
attacks of September 11th accomplished mass destruction without any unconventional
weaponry. If measured strictly in terms of their proven capacity to kill people or the
frequency of terrorist use in the past, CBW weapons are not the most worrisome
Third, the incentives and disincentives for individual terrorists to use chemical
and biological weapons are complex and may not be exactly the same as those that
guide the use of more conventional weapons. Recent suicide attacks indicate, among
other things, an apparently growing willingness on the part of terrorist organizations
to plan and condone the death of their own operatives in the service of the cause. It
is difficult to handle many chemical and biological agents without putting the handler
at risk, especially in the absence of the kind of top-quality equipment that is more
commonly available to states. But instantaneous death in a dramatic explosion is a
far cry from the agony of a slow death from smallpox or exposure to a nerve agent.
Of course, there are many unknowns; but from an individual perspective, the
incentives and disincentives for dying in a CBW attack should not be assumed to be
the same as those that factor into other types of attacks. Indeed, the existence of
20 See Smithson and Levy, “Rethinking the Lessons of Tokyo,” Chapter Three, Ibid., pp.
21 For much more information on this, see CRS Report RL31669, Terrorism: Background
on Chemical, Biological, and Toxin Weapons and Options for Lessening Their Impact, by
22 According to Smithson and Levy, the largest death toll resulting from a single CBW attack
was 19, and in 96 percent of the cases three or fewer people were either injured or killed.
Ataxia, p. xiii.
larger numbers of religious terrorists could actually imply a decreased likelihood of
the use of chemical and biological weapons. Although this point should not be
overstated, violence whose primary aim is to kill as many perceived enemies as
possible may not be likely to employ these agents. It is difficult in most scenarios to
execute an attack with chem-bio weapons that kills a large number of people.
Finally, groups tend to mimic previous successes. Although terrorists do
innovate in various ways,23 groups have most often preferred to use weapons that
have a proven track record. There are no guarantees, but going strictly on the odds
and the historical patterns of terrorist behavior, most experts posit that there is a
higher likelihood that the next major attack will use conventional not unconventional
means. But, again, the caveat is that terrorism seeks to shock.
Issues for Congress
If a chemical or biological terrorist attack were to occur, it is most likely that the
event would be on a small scale physically, with much larger effects on the
population psychologically. For this reason, targets of terrorism are forced to seek
a fine balance: On one hand, it is important to prepare the public for the possibility
of an attack. Among other things, since one of the incentives for using these
weapons is to induce panic, preparations lower the likelihood of their occurrence in
the first place. On the other hand, hyping and publicizing the threat potentially
distorts its probable magnitude and likelihood. This could arguably add to the
incentives for a terrorist organization to attempt an attack.
Additional measures to counter both state and especially non-state means of
proliferation of chemical and biological weapons are crucial to reducing the threat
in the future, both domestically and internationally. This is a difficult technical
challenge in an age of globalization, when the expertise and means to carry out
attacks are becoming much harder to control through traditional state measures like
border controls, export controls, treaties and sanctions. Defensive measures and
consequence management to reduce both the effects of an attack and the incentives
to carry one out will be increasingly important. Within the United States, some
measures enhancing the security of laboratories/facilities have already been enacted.24
Some believe that existing measures are adequate, and others disagree.
With respect to the increasing global availability of information and materials
related to chemical and biological weapons, an important issue could be the fate of
the people who have worked in the Iraqi weapons programs. At this writing, the full
nature of those programs is not publicly known; however, as the United States
forcibly disarms Iraq, it could become critical to ensure that CBW materials and
23 See Paul Wilkinson, “Editor’s Introduction: Technology and Terrorism,” in Technology
and Terrorism (London, England: Frank Cass, 1993), pp. 1-11. Among terrorism experts,
the question of how terrorists use technology, especially the degree to which they innovate
technologically, is complex and contentious.
24 For example, see the USA PATRIOT Act (P.L. 107-5) and the Public Health Security and
Bioterrorism Preparedness and Response Act (P.L. 107-188).
expertise are not disseminated during and after military operations. This is a
potential danger not only with respect to keeping track of the whereabouts and
behavior of the scientists who have been in charge (and may have already been
identified by UNMOVIC and/or U.S. intelligence) but also the production-level
technicians and others who may have access or some degree of knowledge.
At least in the short term, the nightmarish scenario of loss of control of Iraqi
CBW, including potential sale or transfer to terrorist organizations, could arguably
be more likely in an atmosphere of political or economic instability. There might be
incentives for new links to develop between Iraqis who might have benefitted from
the previous regime, and well-heeled groups like Al Qaeda (and its associates).
Osama bin Laden’s expression of support for the Iraqi people (if not the Ba’athist
regime), as well as evidence of Al Qaeda’s existing interest and capabilities, argue
for scrupulous caution along these lines. There have been extensive measures under
the Nunn-Lugar Comprehensive Threat Reduction program oriented toward the
arsenal of the former Soviet Union, but a post-conflict Iraq could present important
new proliferation risks. Existing legislation, including the Iraq Sanctions Act of 1990
and existing provisions under the Chemical Weapons Convention and the Biological
and Toxin Weapons Convention, may not adequately address this new concern,25 and
additional measures targeting this emerging danger may be worth considering.
25 For more information, see CRS Report RL31502, Nuclear, Biological, Chemical and
Missile Proliferation Sanctions: Selected Current Law, by Dianne E. Rennack, and CRS
Report RL31559, Proliferation Control Regimes: Background and Status, by Sharon A.
Squassoni, Steven R. Bowman, and Carl E. Behrens.