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 chemicaland biological weapons themselves have a long history: the first chemical weapons were used inancient Greece; biological weapons have been used in a wartime context since at least the MiddleAges. (1) Employed extensively in the first World War,notably in the use of mustard gas, chemicalweapons have evolved very little in their technology since the mid-twentieth century. Althoughrecent technological advances in biological weapons have been made, the vaccines and treatmentsavailable to deal with some of them have also advanced. Historically, most terrorist groups haveavoided using CBW, in part because they do not want to alienate their own constituencies, and inpart because they have not had the technical expertise to turn them into effective weapons. (2) ThoseCBW attacks that have occurred represent a small proportion of the total number of internationalterrorist incidents. (3) CBW weapons have rarely beenused 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 theJapanese terrorist organization Aum Shinrikyo used the chemical nerve agent sarin on the Tokyosubway, killing 12 people and injuring up to 6,000. The group's efforts, which fell far short of itsgoals, attracted widespread attention and helped increase focus on the so-called weapons of massdestruction (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 hardevidence is limited, a sampling of terrorist groups or individuals that are reported to have shown aninterest in or used chem-bio agents (usually in very limited ways) includes the PKK (KurdistanWorker's Party), believed to have weaponized the nerve gas sarin; HAMAS (Islamic ResistanceMovement), which has reportedly coated shrapnel with poisons and pesticides; numerous U.S.domestic individuals and groups without foreign connections (including the Minnesota PatriotsCouncil, the so-called "Alphabet Bomber," R.I.S.E., Larry Wayne Harris, and others) who have usedor intended to use ricin, plague, anthrax, hydrogen cyanide, sarin, and other agents; and of courseAl Qaeda and its associated groups. (5) But the effortsof Aum Shinrikyo represented a watershed, withits bizarre and seemingly irrational agenda, its systematic pursuit of technical competency, and itsrepeated attempts to kill a large number of Japanese civilians. Even with its multiple technicalfailures, Aum Shinrikyo led to heightened anxiety about the attractiveness and feasibility of futuremass 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 forwhich published data are available), the number of hoaxes went up (from 25 to 603) but the numberof CBW incidents actually decreased (from 48 to 25). (6) Thus it would appear that the fall 2001anthrax attacks in the United States resulted in numerous copy-cat hoaxes, but they did not reflectan overall increase in bioterrorism events. However, terrorism experts continue to worry about theuse of chemical and biological agents. The reasons for increased potential use can be grouped into four major categories: the growthof militant religious groups with political agendas as a percentage of all terrorist groups, theincreasing global availability of CBW information and stockpiles, the internationalization of thethreat of terrorism, and the clear evidence of terrorist interest and capabilities. 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 justover three percent of all identified terrorist groups in 1980 to forty-three percent by 1995. (7) Militantreligious 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 thescruples 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 ofpeople killed and maimed per attack increased. This confirmed the fear of many experts thatterrorism based on extreme religious beliefs, in association with other developments discussedbelow, might be even more dangerous than were the left wing, right wing, andethnonationalist/separatist groups that predominated in earlier years. (8) A larger proportion of theattacks that did occur were executed by persons with religion-based animus. The tragedies ofSeptember 11th seemed to bear out both of these trends. 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 feasibleonly with the resources of a state. Like the rest of the world, terrorist groups have access to the vastamount of technical data disseminated through the Internet. More and more information that mightpreviously have been difficult to collect is becoming easily accessible. Among the groups that havereportedly demonstrated interest in acquiring unconventional weapons (besides Al Qaeda) are thePLO, the Red Army Faction, Hezbollah, the Kurdistan Workers' Party, German neo-Nazis, and theChechens. (9) At the same time, the breakup of theSoviet 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 aglobalized world, and greater availability of materials and expertise in the post-Soviet era, havetogether led to a potentially serious erosion in state control over chemical and biological weapons(or their ingredients). (10) 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-orientedgroups has led to an increased commonality of interests between populations in disparategeographical areas. In part in reaction to American global policies and cultural as well as politicalglobal reach, groups are developing ties across formerly divisive ideological, ethnic, and nationallines. The area of potential recruits is thus broader than it might have been for a traditionalethnonationalist/separatist group supported only by its local constituency, for example. Also, thisinternationalization of the threat has often led to a greater distance between groups and targets. Theresult is not only a removal of moral constraints but also political constraints, with less worry aboutpotentially sullying a homeland or killing potential constituents. Thus, the internationalization ofterrorism may unfortunately imply an increase in just the sorts of incentives that lead groups toconsider 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 along-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 hasreportedly pursued the development of chemical and biological weapons since the early 1990s. (11) In1998, he spoke of acquiring weapons of mass destruction being a "religious duty," and the eleventhvolume of Al Qaeda's 5,000-page "Encyclopedia of Jihad" is devoted to explaining how to constructCBW. (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 amountsof ricin and anthrax at five or six sites, as well as evidence of an interest in plague, cyanide, andbotulinum toxin. (13) In December 2001, CNNobtained a cache of 64 Al Qaeda video tapescontaining gruesome evidence of experiments using an apparent nerve gas against dogs. (14) Furtherafield, in 2002 a reported plot by nine Moroccans to use a cyanide compound to poison the watersupply of the U.S. Embassy in Rome was disrupted; several of the men involved had ties to AlQaeda. (15) In January 2003, a reported plot by sixAlgerians to use ricin was uncovered in a Londonapartment. One of the six arrested had attended Al Qaeda training camps, whereas the others hadreceived training in Chechnya and the Pankisi Gorge region of Georgia. (16) Most recently, evidenceseized in March 2003 with the arrest of operations chief Khalid Shaikh Mohammed demonstratedsurprising technical sophistication, with production timetables and manufacturing specifications forbio-chemical agents, especially weaponized anthrax. (17) In addition to these highly publicizedexamples, there are many other press reports of varying reliability. 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-bioagents are generally more useful for increasing anxiety and panic than causing high numbers ofcasualties. Projections of tens of thousands of casualties are theoretically possible, (18) but many suchestimates are worst-case scenarios likely to occur in hard-to-achieve circumstances, with idealweather 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 causeeconomic damage, or to show strength and increase political support or leverage, or to copy otherterrorist 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 andhype the threat, leading to some of the same outcomes by heightening anxieties. There are a largenumber of practical obstacles to terrorists using these weapons, and these will be discussed next. There are at least four reasons why terrorist groups like Al Qaeda might avoid using chem-bioagents in attacks against the United States and its interests. First and most important, the technicaldifficulties in carrying out such attacks continue to be significant. Aum Shinrikyo is a good exampleof a group that had unusually favorable circumstances for producing chemical and biologicalweapons, 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 fromobtaining biological seed cultures to effectively disseminating them to chemical leaks and accidents,is as easily a warning of the technical challenges involved as it is an example for future groups. (20) For most nonstate actors, difficulties with acquiring materials, maintaining them, transforming theminto weapons, and disseminating them effectively are numerous. While many technical advanceshave occurred in recent years, arguably reducing the barriers somewhat, there are still considerableobstacles to terrorist development of chemical and biological weapons. (21) 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 occasionswhen they have been used, CBW have not resulted in large death tolls, especially compared toconventional weapons such as truck bombs and individual explosive devices. (22) It is worth bearingin mind that the attacks of September 11th accomplished mass destruction without anyunconventional weaponry. If measured strictly in terms of their proven capacity to kill people or thefrequency of terrorist use in the past, CBW weapons are not the most worrisome threat. 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 moreconventional weapons. Recent suicide attacks indicate, among other things, an apparently growingwillingness on the part of terrorist organizations to plan and condone the death of their ownoperatives in the service of the cause. It is difficult to handle many chemical and biological agentswithout putting the handler at risk, especially in the absence of the kind of top-quality equipment thatis more commonly available to states. But instantaneous death in a dramatic explosion is a far cryfrom the agony of a slow death from smallpox or exposure to a nerve agent. Of course, there aremany unknowns; but from an individual perspective, the incentives and disincentives for dying ina CBW attack should not be assumed to be the same as those that factor into other types of attacks. Indeed, the existence of larger numbers of religious terrorists could actually imply a decreased likelihood of the use of chemical and biological weapons. Although this point should not beoverstated, violence whose primary aim is to kill as many perceived enemies as possible may not belikely to employ these agents. It is difficult in most scenarios to execute an attack with chem-bioweapons 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 useweapons that have a proven track record. There areno guarantees, but going strictly on the odds and the historical patterns of terrorist behavior, mostexperts posit that there is a higher likelihood that the next major attack will use conventional notunconventional means. But, again, the caveat is that terrorism seeks to shock. If a chemical or biological terrorist attack were to occur, it is most likely that the event wouldbe on a small scale physically, with much larger effects on the population psychologically. For thisreason, targets of terrorism are forced to seek a fine balance: On one hand, it is important to preparethe public for the possibility of an attack. Among other things, since one of the incentives for usingthese weapons is to induce panic, preparations lower the likelihood of their occurrence in the firstplace. On the other hand, hyping and publicizing the threat potentially distorts its probablemagnitude and likelihood. This could arguably add to the incentives for a terrorist organization toattempt 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 domesticallyand internationally. This is a difficult technical challenge in an age of globalization, when theexpertise and means to carry out attacks are becoming much harder to control through traditionalstate measures like border controls, export controls, treaties and sanctions. Defensive measures andconsequence management to reduce both the effects of an attack and the incentives to carry one outwill be increasingly important. Within the United States, some measures enhancing the security oflaboratories/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 haveworked in the Iraqi weapons programs. At this writing, the full nature of those programs is notpublicly known; however, as the United States forcibly disarms Iraq, it could become critical toensure that CBW materials and 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 ofthe scientists who have been in charge (and may have already been identified by UNMOVIC and/orU.S. intelligence) but also the production-level technicians and others who may have access or somedegree 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 atmosphereof political or economic instability. There might be incentives for new links to develop betweenIraqis 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 theBa'athist regime), as well as evidence of Al Qaeda's existing interest and capabilities, argue forscrupulous caution along these lines. There have been extensive measures under the Nunn-LugarComprehensive 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 WeaponsConvention and the Biological and Toxin Weapons Convention, may not adequately address thisnew concern, (25) and additional measures targetingthis emerging danger may be worth considering.

Summary: 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 andcapabilities, as well as the political fall-out from the war in Iraq. This is a serious present concernthat deserves examination in the broader framework provided by the patterns, motivations andhistorical context for the current terrorist threat. Although it can have a powerful psychologicalimpact, 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 notrend 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 ofCBW weapons against the United States, as well as a brief discussion of issues for congressconcerning how best to counter the threat. It will not be updated.