Encyclopedia of Security and Emergency Management

Living Edition
| Editors: Lauren R. Shapiro, Marie-Helen Maras

Criminals: Terrorist

  • James M. Duggan
  • James J. F. ForestEmail author
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DOI: https://doi.org/10.1007/978-3-319-69891-5_261-3


Terrorist - Extremist perpetrator Radicalized criminal 


Terrorists are criminals who commit or directly support acts of violence in order to achieve some type of sociopolitical objectives.


This chapter examines the groups and individuals who commit or directly support acts of terrorism. The phenomenon of terrorism itself will be covered in other chapters of this volume, including “Terrorism: Domestic” and “Terrorism: International”.” Terrorists are widely considered a distinct type of criminals. They consciously choose to kill, maim and destroy, and also routinely engage in money laundering, theft, fraud, extortion, smuggling (including drugs, weapons, and humans), kidnapping, bank robbery, and many other kinds of criminal activity. But terrorists generally loathe being labeled as ordinary criminals, preferring to use labels like “freedom fighters” or in the case of some religious groups, “holy warriors.” And as described later in this chapter, terrorism is also viewed as a type of political violence.

Generally speaking, terrorists are not crazed killers but instead are usually rational actors who employ terrorist tactics in a calculated effort to magnify their relatively meager resources, draw attention to their plight, and garner support for their cause (Hoffman 2017). Further, the strategic goal of most terrorists is not to kill a lot of people but rather to kill a relatively few and strike fear in the hearts of many, in order to coerce the behavior of a society and its government in ways the terrorists feel will help them achieve their political or social objectives (Forest 2018).

This underscores the communicative aspect of their crimes; unlike many other violent criminals (who tend to avoid the media), terrorists often claim responsibility for attacks and try to justify their violence through their ideology, an articulation of their grievances and goals. There are many different ideological categories of terrorism, including ethnonationalist, left-wing, right-wing, and religious. Within each of these categories, there is a wide spectrum of groups and goals. For example, the category of religious terrorism includes Salafi-Jihadist groups like Al-Qaeda and Islamic State, Shiite militia groups like Hezbollah, Christian antiabortion extremists like the Army of God, and even the Japanese Buddhist cult Aum Shinrikyo. There are also terrorists who use violence on behalf of extreme goals related to environmental protection or animal rights. Each of these ideological categories will be described in this chapter, along with some examples of relevant individuals and groups.

Beyond the ideological dimension, there are also many other differences among terrorists. To begin with, researchers have sought in vain for common attributes among terrorists, but the evidence shows that they can be any age, ethnicity, or religion and from any socioeconomic or educational background (Hoffman 2017; Forest 2018). Both men and women have been terrorists, even suicide bombers (Hoffman 2017; Forest 2018). Some terrorists may have signs of mental illness, but researchers have found nothing that would separate them from other mentally ill individuals who engage in non-terrorist criminal activity (Horgan 2005; McCauley 2007; Corner and Gill 2015). There are also many different roles an individual could play within a terrorist group, from explosive expert to budget manager, logistician, driver, propagandist, and many more (Horgan 2009; Forest 2018). This complicates matters for law enforcement and court systems when trying to prosecute individuals accused of terrorist activity. For example, should a terrorist group’s bomb-maker be treated the same as another member whose role was financial management or document forgery? These and other issues will be addressed in the chapter “Investigations: Terrorism”.

Overall, as this chapter will illustrate, identifying and explaining who is (or is not) a terrorist is not as easy or straightforward as some politicians or media pundits would have us believe. The chapter begins with a brief discussion about the definitional challenges of terrorism and then will review the ideological categories that have motivated most terrorists around the world. Attempts to identify a common demographic profile of terrorists will be reviewed, and examples of particularly prominent terrorists will be used to illustrate the diversity within this category of criminals. Finally, the chapter will conclude with some thoughts about the future of research on terrorists and implications for security and emergency management.

Conceptualizing Terrorism

Terrorism is an extremely complex phenomenon that is open to interpretation and subject to competing opinions among researchers. Consistent with this complexity, there are many definitions of terrorism, not only among individual researchers but also among the various government agencies that contribute to counterterrorism efforts within the USA. For instance, the US Department of State employs the definition provided by Section 2656f(d) of Title 22 of the United States Code, which defines terrorism as “premeditated, politically motivated violence perpetrated against noncombatant targets by subnational groups or clandestine agents,” and the Department of Justice defines terrorism as “the unlawful use of force or violence against persons or property to intimidate or coerce a Government, the civilian population, or any segment thereof, in furtherance of political or social objectives” (Hoffman 2017). Yet another definition is offered by the Global Terrorism Database (GTD), a tool frequently used by terrorism researchers and policymakers, which defines terrorism as “the threatened or actual use of illegal force and violence by non-state actors to attain a political, economic, religious, or social goal through fear, coercion, or intimidation” (Crenshaw and Lafree 2017, p. 23). In general, the diversity of definitions used by scholars and government agencies can be problematic when conducting terrorism research or investigations.

Despite the lack of clarity presented by the various definitions, there are some characteristics of terrorism that are generally accepted by researchers. One of these characteristics is that the violence targets noncombatants, which includes off-duty military and law enforcement, as well as civilians, all of which violates international humanitarian law (Hoffman 2017). In addition, the targeted noncombatant victims of the attack are not the true intended victims of the attack but rather are victimized in order to inflict psychological trauma and “terrorize” the greater society (Horgan 2009). The fear and “terror” inflicted on society are driven in part by the apparent randomness of the attacks and the ferocity of the methods employed, such as beheading hostages and killing women and children (Crenshaw and Lafree 2017).

In addition to being a form of criminal activity that causes psychological trauma, terrorism is also viewed as a type of political violence (along with insurgency, guerilla warfare, rebellion, etc.). Terrorists use acts of violence as a way to achieve some type of political goals. Some may want to overthrow an established government (the classic definition of insurgency), like the Taliban, Al-Qaeda in the Arabian Peninsula, and the Islamic State (Crenshaw and Lafree 2017). Others want the power to control a specific territory (like Hamas or other Palestinian groups) or perhaps even establish an ethnically homogenous “homeland” (like the Basque group ETA in northern Spain). Even religious terrorists are seeking to achieve some kind of political objectives, from establishing an Islamist Caliphate in the Middle East to stopping the practice of abortions in the USA (Forest 2018). Thus, understanding the motives, goals, and objectives of terrorists is necessary for researchers, policymakers, and practitioners.

Motivations of Terrorists

Perhaps the most distinguishing feature of terrorists, compared to other violent criminals, is the nature of their motivations. While other terrorists may carry out acts of violence for profit, revenge, control of drug trafficking routes, and so forth, terrorists articulate their motivations in a broad range of ideological statements. In fact, terrorist groups over the past 120 years have shown a keen interest in shaping perceptions about their activities and efforts to justify their criminal activities as necessary for achieving some preferable future (Forest 2018). There are many categories of ideologies, including ethnonationalist/separatist, left-wing, right-wing, and religious, each of which will be briefly explained below.

The most distinguishing aspect of ethnonationalist/separatist groups is their focus on physical and political geography. The ideology of terrorists in this category is driven by their desire to wrest control of a geographic area from the government in order to establish an independent state for those of a particular ethnicity, like the Chechens in Russia, Kurds in Turkey, Basques in Spain, or Tamils in Sri Lanka. And unlike the ideologies of other terrorist groups, the membership of ethnonationalist/separatist groups is limited by their ethnicity (Forest 2018).

Left-wing terrorists are driven by a utopian vision of a society that provides greater equality through the implementation of a communist government (Forest 2018). Often referred to as Communist, Maoist, or Marxist-Leninist, the ideology of left-wing terrorists is often consistent with Russian revolutionaries who galvanized the working masses to revolt against the government. Left-wing terrorists incite class warfare but are willing to allow anyone to join their cause. While not as common today, left-wing terrorist movements were prominent during the 1960s through 1980s, including the Red Army Faction (RAF) in West Germany, the Red Brigades in Italy, the Weather Underground in the USA, and Sendero Luminoso in Peru.

Right-wing terrorists are often described as either revolutionary or reactionary; the former usually target the government, while the latter may focus on countering the efforts of left-wing movements or threat to the status quo (Forest 2018). For example, the Ku Klux Klan (KKK) became a well-known right-wing terrorist movement in the USA that blocked social reconstruction policies and civil rights in the south. Many right-wing terrorists are anti-leftist, anti-liberal, religiously extreme, anti-government (e.g., the sovereign citizen movement in the USA), anti-gun control, or paramilitary/militia in nature, and some are also racial supremacists (including the Aryan Nations, The Order, Hammerskin Nation, and the American Front), targeting the members of minority groups whom they perceive as a threat.

And finally, the largest and most prominent category of terrorist ideologies today is religious. The past half-century has seen the rise of myriad Christian, Jewish, Sikh, Buddhist, Hindu, and Islamist terrorist groups, all of whom are inspired by the belief that terrorism is necessary to achieve (their interpretation of) God’s will and that the truly pious terrorist is at war with those whose destiny is eternal damnation. From Al-Qaeda and the Islamic State to Hamas (in Israel), Hezbollah (in Lebanon), or the Army of God (a violent antiabortion movement in the USA), religious terrorists have much in common. More than other categories of terrorists, the religious extremists are absolutist (you are either with them or the enemy, there are no innocent bystanders) and supremacist (their interpretation of the faith is the one and only truth). This combination often means a negotiated compromise to address their grievances is impossible.

This category also includes some of the only examples of terrorists who have engaged in attacks using weapons of mass destruction. For example, Aum Shinrikyo was a Japanese religious cult that integrated elements of esoteric Buddhism, Hinduism, messianic Christianity, and apocalyptic prophesies. In 1995 Aum Shinrikyo launched a sarin nerve agent attack on a Tokyo subway that left a dozen dead and more than 3000 injured. Another religious cult, the Rajneeshes, used salmonella to poison a local population in the state of Oregon. And most recently, the Sunni jihadist group Islamic State used chemical weapons (including chlorine, phosphine, and mustard agents) dozens of times in Iraq and Syria over a 4-year period. Of all the terrorist groups currently threatening civil societies worldwide, religious terrorists account for an overwhelming majority.

These various ideologies shape a terrorist group’s recruitment efforts, tactics, and targets. For example, left-wing terrorists typically target government buildings and centers of capitalism, as well as symbols of authority and power, such as police stations, politicians, industry, and military facilities. Meanwhile, animal rights extremists will target animal research laboratories and the businesses that finance them, and right-wing groups will target members of a minority population or perhaps a synagogue. Similarly, an attack against a particular target will likely indicate the type of ideology motivating the group or individual responsible for that attack.

Throughout these ideological categories, some common themes can be identified. First, the grievances articulated by the terrorists often include some complaint about government legitimacy (or lack thereof). According to Ted Robert Gurr’s theory of relative deprivation, (Gurr 2016 [1970]), the risk of political violence in a country rises as the perceived legitimacy of a government declines. Contributing factors to perceived illegitimacy of a government include corruption, repression, indiscriminate violence, and incompetence. Sometimes, a terrorist group will carry out violent attacks in order to provoke a violent overreaction by the government in order to negatively impact the legitimacy of the regime and generate more support for the terrorist group.

Other grievances that could motivate an individual toward terrorism include structural disadvantages that exclude particular segments of a society from economic, educational, or political opportunities or the provision of social services. These contribute to a gap between an individual’s aspirations for a better life and opportunities to achieve those aspirations, generating significant frustrations. However, the research also indicates that the most poverty-stricken regions of the world are no more likely to spawn terrorists than a wealthy country. In fact, there are many impoverished areas of the world that have produced no terrorists, while a significant number of today’s jihadists and right-wing terrorists were raised in affluent neighborhoods, went to college, and even became engineers and physicians (Forest 2018). The broad range of personal grievances and frustrations, in turn, help explain why the majority of terrorist attacks worldwide are domestically oriented – that is, they are perpetrated by citizens or residents of the country in which the attack occurs. Despite what today’s overhyped media coverage and political rhetoric about international terrorism suggest, domestic contexts have always had a far more powerful impact on motivating a person toward terrorist activity.

Another common dimension among many religious, ethnonationalist, and right-wing terrorists is “othering,” loosely defined as identifying a specific population or subgroup (e.g., Jews, Protestant loyalists, blacks, “infidels,” etc.) as the primary source of evil. Adherents of right-wing terrorism are driven by a particularly strong sense of “othering” that dehumanizes those they perceive of as their enemy, while the “othering” component of religious terrorism is even more radical and contributes to their zero-sum worldview.

Overall, because terrorism is a highly contextual phenomena, we must consider the socioeconomic, political, and cultural environment that contributed to the motives of an individual to engage in terrorist activity. When examining incidents of terrorism, we must remain cognizant of the fact that terrorism does not occur in a vacuum; there is a constant interplay of myriad socioeconomic and political factors, as well as interpersonal relationships and group dynamics that provide for the environment in which individuals make rational choices. Further, it is important to remember that individuals from virtually all walks of life have been drawn into terrorist activity.


While motivations may be the most central element separating terrorists from other kinds of violent criminals, some politicians and media pundits have attempted to portray a certain type of individual as most prone to being a terrorist. In today’s politically charged environment, personal characteristics such as young, Arab, male, and immigrant have been misappropriated by some as proxy representations of the terrorist threat within the USA. And yet, nearly five decades of research by thousands of scientists and scholars have found no evidence of any common personal traits or characteristics that would help us predict the likely risk of involvement and engagement in terrorist activity (Horgan 2005). Instead of a common terrorist profile, the evidence reinforces the point made earlier in this chapter: individuals consciously choose whether to perpetrate or support acts of terrorism. Further, individuals from virtually any background can choose to engage in terrorist activity.

Some researchers have questioned whether mental illness might play a role, arguing that surely only crazy people would be able to justify to themselves the horrific crimes inflicted by terrorists upon innocent civilians (McCauley 2007). And yet, empirical research indicates that terrorists are rarely mad, very few suffer from personality disorders, and there is little evidence that terrorists are suffering from psychopathology (Hoffman 2017; McCauley 2007; Silke 2004). In fact, research has shown that terrorist organizations most often shun those who display any signs of mental illness, unless there is a specific tactical use for them – for instance, the Provisional IRA, or PIRA, employed the mentally ill to beat up members who got out of line but would not deploy them in an ordinary operational capacity (Horgan 2009).

One exception to this body of research may be found among terrorists who carry out attacks without the direct involvement of an established organization – the so-called “lone wolf” phenomenon. For example, a recent study (Corner and Gill 2015) suggests that terrorists who are not members of an organization are more likely to suffer from mental illness than members of the broader population. Further, they found that lone actor terrorists were significantly more likely to suffer mental illness than terrorists who were members of an established group. More research in this area is needed, but the study reflects an important modern challenge for security and emergency management professionals: how to respond to the lone actor terrorist.

Forest (2018) prefers the term “do-it-yourself” terrorists rather than “lone actor” or “lone wolf,” as true lone actors are extremely rare. In this description, the do-it-yourself terrorist is one who has not had any direct operational support or training from an established terrorist group but was simply inspired to plan and execute a terrorist attack entirely on their own. While a terrorist group’s ideology may provide them with a perceived justification for the act of violence, the individual chooses the target, weapons, and timing for the attack. During the late 1880s through the early 1900s, a wave of anarchists in Europe and the USA were the most prominent form of do-it-yourself terrorism, but more recent examples in the USA include the 1995 bombing of the Murrah Federal Building in Oklahoma City by Timothy McVeigh and the 1996 bombing of the Atlanta Olympics by Eric Rudolph, both of whom are considered right-wing terrorists in the research literature. And the last two decades have seen the rise of the do-it-yourself jihadists, inspired by the leaders of Al-Qaeda or the Islamic State to carry out terrorist attacks in Europe and the USA. Some well-known examples include Nidal Hasan’s attack at Fort Hood in 2009, the attempted attack against the New York subway by Najibullah Zazi and two of his friends that same year, the Tsarnaev brothers’ attack against the Boston Marathon in 2013, and the mass shooting at an Orlando nightclub by Omar Mateen in 2016. The diversity of backgrounds and motivations among do-it-yourself terrorists reinforces the central fact that a common “terrorist profile” is inherently elusive. As a result, the question of who becomes a terrorist and why can only be answered by analysis that includes a broad range of contextual factors and influencers.

Terrorist Methods

Many kinds of crimes have been considered acts of terrorism when perpetrated by individuals pursuing some kind of sociopolitical agenda, as described above. One of the most common forms of terrorism has involved bombings against a wide range of targets, from public transportation to hotels, government buildings, and marketplaces. The bombs used in these attacks vary widely in size and sophistication, from the donkey cart, gunpowder, and shrapnel used by the anarchist Mario Buda in the 1920 Wall Street bombing to the two backpack pressure cooker bombs used by the Tsarnaev brothers in the 2013 Boston Marathon attack. Recently the highly unstable chemical explosive triacetone triperoxide (TATP) has been used in several jihadist terrorist attacks including the July 2005 bombing of the London Underground, the 2015 Paris attacks, the 2016 Brussels attack, and the 2017 Manchester attack. Since the introduction of suicide bombers by the Lebanese terrorist group Hezbollah in the early 1980s, there has been a global proliferation of this distinct method of delivering the explosives to the target (Hoffman 2017; Forest 2018). While the ethnonationalist group Tamil Tigers in Sri Lanka were the world’s leading suicide bombers during the 1990s, we have since seen a global proliferation of this tactic involving mostly jihadist groups from Nigeria and Somalia to Pakistan and Afghanistan. Some of these groups have even deployed women and young children as suicide bombers (Forest 2018).

Beyond explosives, terrorist attacks have included a variety of other weapons, as demonstrated by the 2017 knife attack at London Bridge, ramming vehicles into crowds (e.g., Nice, 2016, and New York City, 2017) or intentionally crashing commercial airplanes into buildings (September 11, 2001). Terrorists have also engaged in kidnapping and hostage-taking for over a half-century, sometimes to bargain for policy concessions or an exchange of prisoners (e.g., the Red Army Faction during the 1970s) but increasingly to demand sizable monetary ransoms (e.g., the Abu Sayyaf Group and Al-Qaeda in the Islamic Maghreb, among several others). In Iraq and Syria, terrorists have posted videos online showing them beheading a number of western hostages as a warning to their enemies. This reflects one of the most important factors that distinguish acts of terrorism from other criminal acts – taking credit for the violence is part of the communicative strategy of terrorism. Today, terrorists used video cameras and social media to amplify the impact of their attacks as a way of generating more fear among the general public, in the belief that this will help them achieve the sociopolitical goals of their terrorist movement.


Obviously, nobody is born to be a criminal or terrorist. Terrorism is a type of deviant criminal behavior that is learned and can be motivated by a broad range of goals, contexts, and individuals. Much of the research on terrorist motivations has focused on an individual’s perceptions, like “perceived legitimacy of the regime,” “perceived threat,” or “perceived opportunities.” This underscores the simple fact that virtually anyone – under the right conditions – can become convinced to perpetrate or support acts of terrorism. Further, in addition to the impact of their surrounding contextual factors (political, socioeconomic, etc.), an individual’s decision to engage in terrorism is influenced by friends, colleagues, terrorist group leaders, radical clerics, or even family members.

Terrorists are a distinct subcategory of criminals, defined by the sociopolitical nature of their motivations, and they engage in much more than just violent forms of criminality, to include drug smuggling, money laundering, theft, kidnapping, and much more. Security policies and strategies to combat terrorism require a broad range of intelligence and law enforcement actions as well as relevant socioeconomic policies that address the underlying contextual factors motivating the terrorists.



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Further Reading

  1. Abrahms, M. (2008). What terrorists really want: Terrorist motives and counterterrorism strategy. International Security, 32(4), 78–105.CrossRefGoogle Scholar
  2. Forest, J. (2018). The terrorism lectures (3rd ed.). Santa Ana: Nortia Press.Google Scholar
  3. Hoffman, B. (2017). Inside terrorism (3rd ed.). New York: Columbia University Press.CrossRefGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Center for Terrorism and Security StudiesUniversity of Massachusetts LowellLowellUSA