Politically motivated terrorists who desire to change societies rather than destroy them might avoid killing very large numbers of people because the political costs would exceed the benefits.10 Some terrorists, however, want to annihilate their enemies or demolish the societal order. William Pierce, leader of the neo-Nazi organization National Alliance, aims to initiate a worldwide race war and establish an Aryan state. "We are in a war for the survival of our race," he explains, "that ultimately we cannot win... except by killing our enemies... It's a case of either we destroy them or they will destroy us, with no chance for compromise or armistice."11 Creating social chaos is thus a worthwhile objective in Pierce's view. Ramzi Yousef, organizer of the World Trade Center bombing, claimed he was exacting revenge against the United States.12 Osama bin Laden seems to have similar motives.

Terrorists may want to impress their target audience with high technology or with weapons that appear more sophisticated than conventional ones. Terrorists may find technology appealing for various reasons. William Pierce, who studied physics at California Institute of Technology, is interested in high-technology weapons. In his novel The Turner Diaries, right-wing extremists use nuclear, chemical, biological, and radiologic weapons to take over the world. Pierce believes he can attract more intelligent recruits to his organization over the Internet than through radio or leaflets.14

Domestic extremists have shown greater interest in chemical and biological weapons in the last 5 years. For example, in 1998, members of the Republic of Texas were convicted of threatening to assassinate with biological agents President Clinton, Attorney General Janet Reno, and other officials.15 In May 1995, 6 weeks after the Aum Shinrikyo incident on the Tokyo subway, Larry Wayne Harris bought three vials of Yersinia pestis, the bacterium that causes bubonic plague. No law prohibited Harris or any other U.S. citizen from acquiring the agent. The law has been tightened up since, although many fear it is still not restrictive enough. The Federal Bureau of Investigation (FBI) Director Louis Freeh reports that "a growing numberwhile still smallof `lone offender' and extremist splinter elements of right wing groups have been identified as possessing or attempting to develop or use" weapons of mass destruction.16

In February 1998, Harris boasted to an informant that he had enough military-grade anthrax to wipe out all of Las Vegas. Eight bags marked "biological" had been found in the back of a car he and his accomplice were driving.17 Several days later, federal authorities learned that the anthrax Harris had brought to Las Vegas was a vaccine strain not harmful to human health. Nevertheless, the incident frightened many people and sparked a proliferation of anthrax hoaxes and threats in the second half of 1998 continuing into 1999 by groups including Identity Christians and other antigovernment groups, extortionists, antiabortion activists, and presumed prochoice groups. In many cases, the perpetrator's motives were unknown, but some incidents appear to have been student pranks, demonstrating the extent to which the threat of anthrax has entered U.S. consciousness (Table).

With the end of the cold war and the breakup of the Soviet Union, weapons of mass destruction and their components have become easier to acquire. Underpaid former Soviet weapons experts may be providing biological weapons and expertise to Iran.18 South African biological weapons scientists have offered their expertise to Libya.19 State-sponsored groups are most capable of overcoming technical barriers to mass-casualty attacks, but the sponsor would presumably weigh the risk for retaliation before supporting this type of terrorist attack.

College-trained chemists and biologists could presumably produce biological agents, although they might have trouble disseminating them as aerosols. Microorganisms can be disseminated by air in two forms: as liquid slurries or as dry powders. While producing liquid slurries is relatively easy, disseminating them as respirable infectious aerosols over large open areas is not. Although dry powders can be disseminated far more easily, high-quality powders require substantial development, involving skilled personnel and sophisticated equipment. Milling biological agents would require a level of sophistication unlikely to be found among many domestic terrorist groups. Far more likely are low-technology incidents such as contaminating foods, poisoning livestock, or disseminating industrial poisons in an enclosed space. Such attacks could still be lethal. Major attacks cannot be ruled out; however, governments need to prepare.

In the mid-1980s, a little-known survivalist group called The Covenant, the Sword, and the Arm of the Lord (CSA) acquired a large drum of cyanide with the intention of poisoning water supplies in major U.S. cities. At the time, CSA was unusual among terrorist groups in that its sole objective was large-scale murder rather than influencing government policies. CSA overcame two of three large obstacles to successful employment of a chemical agent. It had the motivation to use a chemical agent to kill large numbers and no political or moral constraints. The group had acquired a chemical agent, although not in sufficient quantity to contaminate city water supplies. The group's leaders had not recruited technically trained personnel and chose an unworkable dissemination technique. Moreover, the group lacked discipline and was easily penetrated by FBI. It is unlikely that CSA would make such mistakes if it were operating today, when antigovernment groups are so much more aware of the potential of poison weapons for inflicting mass casualties.20

CSA was run as a relatively open compound. Some members wrote articles in local papers espousing antigovernment beliefs, and some worked in neighboring towns. Several former CSA members became informants, often because they hoped to get their sentences reduced for other, unrelated, crimes. In recent years, however, antigovernment groups have become more aware of the danger of penetration by law-enforcement authorities and have devised a new way of organizing themselves called "leaderless resistance."21 Members are encouraged to act on their own, minimizing their communication with the leadership of the movement. Timothy McVeigh operated according to this model. His bombing of the Oklahoma City Federal Building was originally conceived of by CSA, although it is not clear that McVeigh knew of CSA's earlier plot. If future terrorists with chemical or biological agents act on their own or in small, secretive groups, FBI may have difficulty apprehending them.

One of CSA's objectives was to establish a computerized, nationwide system linking right-wing groups. This goal has been achieved, although CSA is not exclusively or even principally responsible for this achievement. The nationwide linking of right-wing groups has implications that have not been adequately appreciated by the law enforcement community. The Internet makes terrorist acts easier to carry out. It facilitates leaderless resistance by allowing leaders of the movement to communicate with sympathizers worldwide without having to meet face-to-face with their followers.

A small but growing number of domestic terrorists could attempt to use biological weapons in the belief that doing so would advance their goals. The most likely are religious and extreme right-wing groups and groups seeking revenge who view secular rulers and the law they uphold as illegitimate. They are unconstrained by fear of government or public backlash, since their actions are carried out to please God and themselves, not to impress a secular constituency. Frequently, they do not claim credit for their attacks since their ultimate objective is to create so much fear and chaos that the government's legitimacy is destroyed. Their victims are often viewed as subhuman since they are outside the group's religion or race.

Religiously motivated groups are increasing. Of 11 international terrorist groups identified by the Rand Corporation in 1968, none were classified as religiously motivated. By 1994, a third of the 49 international groups recorded in the Rand-St. Andrews Chronology were classified as religious.22 Religious groups are not only becoming more common; they are also more violent than secular groups. In 1995, religious groups committed only 25% of the international incidents but caused 58% of the deaths.23

Identity Christians believe that the Book of Revelation is to be taken literally as a description of future events. Many evangelical Protestants believe in a doctrine of rapture: that the saved will be lifted off the earth to escape the apocalypse that will precede the Second Coming of Christ. Followers of Christian Identity (and some other millenarian sects), however, expect to be present during the apocalypse.24 Because of this belief, some followers of Christian Identity believe they need to be prepared with every available weapon to ensure their survival.

Organizational pressures could induce some groups to commit extreme acts of violence. Followers tend to be more interested in violence for its own sake than in the group's purported goals, making them less inhibited by moral or political constraints than the leaders. Leaders may have difficulty designing command and control procedures that work. Offshoots of established groups may be particularly dangerous. Groups may also become most violent when the state is closing in on them, potentially posing difficulties for those fighting terrorism. Another factor is the nature of the leader. Charismatic leaders who isolate their followers from the rest of society often instill extreme paranoia among their followers. Such groups can be susceptible to extreme acts of violence.

Asked who he thought the most likely domestic perpetrators of biological terrorism were, John Trochman, a leader of the Montana Militia, said that extremist offshoots of Identity Christian groups are possible candidates, as are disaffected military officers.25 Some antigovernment groups are attempting to recruit inside the U.S. military.26 William Pierce also foresees the use of biological weapons by antigovernment groups. "People disaffected by the government include not only the kind of people capable of making pipe bombs. Bioweapons are more accessible than are nuclear weapons."27

Terrorism with biological weapons is likely to remain rare. This is especially the case for attacks intended to create mass casualties, which require a level of technologic sophistication likely to be possessed by few domestic groups. While state-sponsored groups are most likely to be capable of massive biological weapons attacks, the state sponsor would presumably have to weigh the risk for retaliation. As in the case of other low-probability high-cost risks, however, governments cannot ignore this danger; the potential damage is unacceptably high. Because the magnitude of the threat is so difficult to calculate, however, it makes sense to focus on dual-use remedies: pursuing medical countermeasures that will improve public health in general, regardless of whether major biological attacks ever occur. This would include strengthening the international system of monitoring disease outbreaks in humans, animals, and plants and developing better pharmaceutical drugs.

The risk for overreaction must be considered. If authorities are not prepared in advance, they will be more susceptible to taking actions they will later regret, such as revoking civil liberties. Attacks employing biological agents are also more likely and will be far more destructive if governments are caught unprepared.