Single Actor Terrorism: Scope, Characteristics and Explanations

Single Actor Terrorism: Scope, Characteristics and Explanations

by Petter  Nesser


This Research Note does three things. First, it takes a critical look at definitions, conceptualizations and empirical observations within the field of individual terrorism. Second, it presents and problematizes empirical surveys of so-called “lone wolf terrorists” and individual jihadist terrorists in Europe. Third, it discusses alternative theoretical arguments regarding the scope, characteristics and possible increase of single actor terrorism. Existing research indicates that single actor terrorism is likely to remain a relatively marginal phenomenon, but that attacks may become more sophisticated and deadly due to contagion and tactical diffusion via the Internet, mass media and social networks. Regardless, the analysis presented in the following reveals an acute need for clearer operationalizations and better data in the study of individualized terrorism.



The attacks by Anders Behring Breivik in Norway and Mohammed Merah in France demonstrated that single terrorists may cause devastating effects. The attacks also taught us that it is highly difficult for law enforcement to prevent such attacks. What is single actor terrorism? What is the scope of single actor terrorism? What drives single actor terrorism? Is single actor terrorism more dangerous than other types of terrorism? Is the phenomenon a growing trend? While individual terrorist attackers have received considerable media attentions over the last couple of years, academic research on the topic remains relatively sparse.



Terrorism is usually defined and understood as a group phenomenon. Organisation and group dynamics are seen as important conditions for violent radicalisation and features distinguishing political terrorists from lunatic killers. In the terrorism research literature, terrorist attacks by single actors are usually portrayed as “lone wolf terrorism” (Spaaij 2012), “leaderless resistance” (Kaplan 1997) or “solo terrorism” (CTA 2011).[1] There is no consensus regarding the definition of these concepts, something that constitutes an analytical obstacle. Leaderless resistance is perceived as a military strategy by terrorist organisations under pressure. The strategy is characterized by asymmetric warfare and terrorist attacks by horizontal networks of small cells, or individuals who minimize interaction with organisational entities and a central command. Lone wolf terrorism is usually understood as terrorist attacks undertaken by individuals operating independently from organised groups. We will get back to the term solo terrorism.

The strategy of leaderless resistance is usually traced back to 19th century anarchists who staged political assassinations and bombings under the slogan "propaganda by deed" (Woodcock 1962).[2] Many of these terrorist attacks were perpetrated by single individuals. After World War II, ideas about leaderless resistance gained ground among American anti-Communists as a means of fighting Soviet allies in Eastern Europe and Latin America.[3] Then, during the 1980s and 1990s American white supremacists revived ideas of leaderless resistance, when the U.S. government cracked down on domestic racist movements. For example, Ku Klux Klan leader Louis Beam (1992) prescribed a strategy of small “phantom cells” or individuals guided by a common ideology and operating without any form of central command, as the only way for American “patriots” to prevail against the Federal Government’s “tyranny”.[4]  Under the pseudonym Andrew McDonald, the American Neo-Nazi William Luther Pierce (1978, 1989) wrote fictional books portraying future terrorist campaigns by ideologically driven terrorist cells and individual terrorists against foreigners, pro-immigration spokespersons, and government targets.[5] In the same vein white supremacist Tom Metzger introduced the term "lone wolfism" to popularize the image of the lonesome, “patriotic” warrior.[6]

In the late 1990s, one of Al-Qaeda’s strategic thinkers, Abu Musab al-Suri, presented a military theory for the jihadist movements bearing striking similarities to the concepts developed among anti-Communists and white racists. Al-Suri called upon jihadist movements under pressure and not controlling territories to engage in leaderless guerrilla warfare and “individual terrorism jihad” while awaiting conditions in which “open front” insurgency and military campaigns could succeed.[7] For al-Suri such a strategy was suboptimal, but necessary, and implied shadowy “cell builders” representing the movement and preparing small cells or individuals for operations, but disappearing before attacks were launched.[8] In recent times, an Al-Qaeda organisation facing tremendous pressures has called for individual attacks by sympathizers worldwide in statements by its leadership as well as in the Inspire magazine issued by its Yemen branch. This magazine has led a campaign recommending solo terrorism and providing operational advice.[9] Coinciding with a renewed focus on "individual terrorism jihad" among Al-Qaeda  and affiliates, from around 2008 onwards there has been a marked increase in international terrorist attacks by individual jihadists.

While a number of studies have addressed the ideational and strategic foundations of leaderless resistance by anarchists, right-wing racists, jihadists and other extremist camps (Kaplan 1997, Borum 2005, Sageman 2008) [10], there is a small but growing body of research (Spaaij 2010 and 2012, Bakker & de Graaf 2010, Pantucci 2011) focusing more on operational and motivational aspects of terrorism by single individuals or lone wolves.[11] However, there is considerable confusion with regards to definitions and operationalizations.
Lone wolves are mostly defined as individual terrorists operating in isolation from organised networks (Spaaij 2012; COT 2007). Yet, at other times lone wolves are defined more widely as terrorists executing attacks on their own, but having various types of contacts with organised extremists during the radicalisation process. The nature of such contacts is poorly specified, as is the level of organisation required for there to be an organisational link.
The analysis unit of the Danish Police Intelligence service, CTA, introduces a distinction between lone wolves and solo terrorists, the former operating in isolation and the latter having ties to violent extremist or terrorist networks. CTA further differentiates between bottom-up and top-down solo terrorists, the former implying self-recruited individuals connecting with organised networks for assistance and inspiration, and the latter implying individuals recruited, trained and controlled by terrorist networks. The CTA does provide some, albeit vague clues on how to distinguish true single actors from those operating in group contexts. Pantucci (2011) offers the widest definition of lone wolves, even including small terrorist cells consisting of two or more persons acting independently from organisations.[12]

Below is an attempt to illustrate the relationship between categories of individualized terrorism:


This lack of mutually exclusive categories and clear operationalizations makes it hard to draw firm conclusions from empirical research on single actors; are we talking about a distinct phenomenon or a variant of group terrorism? The lack of coherent coding to produce reliable micro-level data further complicates the matter. The author will exemplify.


Scope and characteristics

We now turn to empirical patterns of single actor terrorism. A 2012 study by Ramon Spaaij offers the most comprehensive empirical survey of lone wolf terrorism to date. He collects data from the Terrorism Knowledge Database (TKB) and Global Terrorism Database (GTD) on single actor terrorist attacks in selected Western countries between1968 and 2010.[13] Spaaij identifies 88 lone wolves responsible for 198 attacks. The study presents general statistics based on 88 cases and five in-depth case studies of well-known cases.[14] Spaaij acknowledges that GTD and TKB data imply methodological pitfalls. The study employs a strict definition of lone wolf terrorism and excludes individuals linked to organised networks. Spaaij admits that, given the data, the distinction is difficult to draw in practice.

He mentions Timothy McVeigh who bombed a government building in Oklahoma in 1995 and Richard Reid who tried to down a trans-Atlantic airliner in 2001 as examples on cases left out. McVeigh received assistance from his comrade Terry Nichols and had ties to organised white supremacists, whereas Reid was acting on orders from Al-Qaeda. Spaaij also acknowledges that many of the cases included in his survey involve obscure circumstances, and that closer investigations could reveal types of interaction with organised actors that could affect his incident count. According to Spaaij’s statistics, lone wolves are behind 1.8 % of the total number of 11.235 terrorist attacks in the selected countries, constituting a marginal trend. He identifies a marked prevalence of the phenomenon in America compared to Canada, European countries and Australia. [15] The study further identifies an overall, gradual increase in lone wolf attacks. The increase is more pronounced in Europe than America, and there were spikes in the overall occurrence of attacks during the early 1980s, early to mid-1990s and early 2000s.

With regards to ideological motivation, the survey attributes 17% of lone wolf attacks to right-wing racists, 15% to Islamists, 8% to anti-abortion extremists, and 7% to national-separatists.[16] More than 30% of the cases were categorized as “other” or “unknown” in terms of motivational drivers. The prevalence of right-wing militancy and Islamism stands in contrast to longitudinal surveys of terrorist trends, in which nationalist-separatist terrorist groups dominate the picture.[17] Spaaij’s survey further finds that lone wolves typically attack soft civilian targets (58%), officials and politicians (13%), health personnel (10%), and that they (just like group terrorists) seek to maximize symbolism. As for weapons, most employed firearms (43%), 28% utilized explosives, 16% conducted armed hijackings and 6% committed arson.

The use of firearms was more prevalent in the United States and Spaaij indicates U.S. gun laws and the popularity of the leaderless resistance strategy among American racists as possible explanations. He compares lone wolves’ use of firearms to terrorist groups, who employ explosives in 65-75% of cases registered in databases. According to Spaaij’s statistics lone wolf terrorism is not very lethal, only resulting in 0, 6 deaths per incident. The lethality does not increase significantly in the time period surveyed. Of the five in-depth case studies undertaken by Spaaij, three utilized bomb devices and two used guns. Two targeted politicians whereas three attacked specified groups of civilians such as immigrants or random victims.
Based on micro-level analysis of well-known cases, Spaaij observes that lone wolves’ radicalisation processes tend to involve interaction with broader ideologies and movements, and a particular mix of personal frustrations and ideology, in which subjects use the latter to explains the former.[18] He also emphasizes how mental problems and social inabilities appear to be overrepresented among lone wolves, showing how they struggle with fitting to group environments and tend to isolate themselves.[19] Sociologically, Spaaij finds that lone wolves come from a variety of backgrounds, but tend to be well-educated and self-taught with regards to extremist ideology and terrorist tactics.
While Spaaij’s lone wolf study is an important contribution, some comments are in order. First, the databases used almost exclusively register successfully committed attacks. Given the fact that terrorist plots often fail or get thwarted, and that this may apply disproportionally to single actors, failed plots should also be taken into consideration. Furthermore, as acknowledged by Spaaij, several of the cases in the study may appear as lone wolf terrorism while in fact having substantial network ties. Also, the inclusion of failed and thwarted terrorist plans, as well as the recent attacks in Norway could seriously affect prognoses regarding lethality of lone wolf attacks and reveal greater variance in operational patterns. Moreover, the study does not compare the level of lone wolf terrorism to variations in the totality of incidents across time. Last, the observations regarding psychological and social profile seem to rest profoundly on five out of 88 cases, - cases that appear to involve more clear-cut lone wolves than the other sample cases, something that raises questions about validity.

For comparison, this author conducted a survey of single actor jihadists in Western Europe between 1995 and present. [20] The following outlines the main findings from that survey before discussing alternative explanations for the occurrence of single actor terrorism. Incidents were drawn from an open source chronology of planned, prepared and executed terrorist attacks by jihadists in Western Europe, which has been maintained by the author since 2003.[21] 

Out of a total of 105 of planned, prepared and executed terrorist plots by jihadist actors between 1995 and 2012 (based on the latest count), as much as 15 (14%) cases involved individual attackers.  The cases included:

  1. “Shoe-bomber” Richard Reid’s attempt to down a trans-Atlantic jet in 2001.
  2. An Iraqi sending toxic letters to the prime minister’s office and the U.S. and Saudi embassies in Belgium, 2003.
  3. Dutch-Moroccan Mohammed Bouyeri’s assassination of Theo Van Gogh in 2004.
  4. “Wannabe” jihadist Nicholas Roddis’ 2007 bomb plans and hoax in the UK.
  5. British convert Andrew Ibrahim’s 2008 plan to bomb a shopping center in Bristol.
  6. British convert Nicky Reilly’s 2008 attempt to bomb a restaurant in Exeter.
  7. Libyan Mohammed Game’s 2009 attack on a U.S. military base in Milan.
  8. Nigerian Umar Farouk Abdulmutallab’s attempt to down a trans-Atlantic jet in 2009.
  9. Danish-Somali Mohammed Geele’s attempt to assassinate Kurt Westergaard in Denmark, 2010.
  10. Bengali Rajib Karim’s plot to down a trans-Atlantic jet in 2010.
  11. British-Pakistani Roshonara Choudry’s 2010 attempt to assassinate British MP Stephen Timms.
  12. Chechen Lors Doukaiev’s 2010 plan to bomb Jyllands-Posten newspaper in Denmark.
  13. Swedish-Iraqi Taimour Abdulwahab al-Abdaly who launched an unsuccessful suicide bombing in Stockholm, 2010.
  14. Kosovar Arid Uka who shot and killed two U.S. soldiers at Frankfurt airport in 2011.
  15. French-Algerian Mohammed Merah who killed French soldiers and attacked a Jewish children’s school in France, 2012.

My survey did not distinguish between lone wolves and solo terrorists, but I found that four out of the 15 cases appeared to be disconnected from organisations and identifiable networks of extremists. [22]

Furthermore, I found that only three of the 15 cases preceded 2008, making the phenomenon almost non-existent before that time, and the relative increase compared to the total number of terrorist plots between 2008-2012 significant (2008: 2/8 incidents, 2009: 2/5 incidents, 2010: 5/13 incidents, 2011: 1/3 incidents, 2012:1/4 incidents).[23] 

In terms of operational patterns, approximately 50% of the cases involved mass casualty bomb attacks against civilians, three of them suicide missions against airplanes. Three cases involved assassinations of public figures (such as the Danish cartoonist Kurt Westergaard, British MP Stephen Timms and Dutch filmmaker Theo Van Gogh) with handgun, knife and axe. Three cases involved attacks on soft military targets using handguns or explosives. [24]

My survey thus found that there was a higher occurrence of single actor attacks among jihadists than in the broader population surveyed by Spaaij, and that jihadist loner attacks were potentially more deadly. Although most of the jihadists in my sample seemed connected to extremist environments and received assistance, encouragement or instructions, I found some support for Spaaij’s observations about motivations and socio-psychological profiles. In my sample, one person was diagnosed with Asperger syndrome and several had mental health issues or behavioral disorders. [25]

Also people like the shoe bomber Richard Reid and the Chechen Lors Doukaiev who tried to launch a bomb attack in Denmark avenging the Mohammed caricatures came from troubled family backgrounds and had dropped out of the educational system. Furthermore, in several cases, personal frustrations appear to have been an important factor behind the ideological radicalisation as suggested by Spaaij’s lone wolf research. For example, it has been alleged that Mohammed Bouyeri’s failure to fulfill the dream of establishing a youth club for immigrants played a central part in his radicalisation process.[26]

The author’s survey of individual jihadists encountered the same definitional challenges as the lone wolf study, but due to the limited scope of the study (one type of actor, limited time period), and the magnitude of updated press information about jihadist terrorism, the survey is based on more, and more reliable data, and may, with a relatively high level of precision, determine the relationship between single actor and group terrorism by jihadists in Europe.

Whether my findings have validity beyond the jihadism in Europe case is another question. To reach more valid and generalizable knowledge about single actor terrorism, there is definitively a need for better data sets which include both successful and foiled terrorist plots by diverse ideological trends. We also need to find better ways to distinguish clearly between those few true lone wolves who operate in total isolation and single actors operating on behalf of organised groups. Despite definitional obstacles and weaknesses of empirical data, the existing research does provide a sound basis for discussing alternative hypotheses regarding the scope and nature of single actor terrorism, which we will turn to now.




Studies of lone wolf terrorism hypothesize that the occurrence of the phenomenon varies according to trends in ideologies and strategic thinking. Spaaij identified peaks in the occurrence of lone wolf terrorism in the 80s when American right-wing thinkers focused on leaderless resistance and “lone wolfism,” and in the early 2000s after jihadists picked upon similar ideas during the late 1990s, as exemplified by Abu Musab al-Suri’s strategic writings.
The thesis is backed by anecdotal evidence that Timothy McVeigh and several other right-wing terrorists possessed writings by William Pierce’s and acted according to advice in American rightwing fanzines.[27] Similarly several jihadists who plotted individual attacks in Europe and the U.S. appear to have been influenced by Al-Qaeda in the Arabian Peninsula (AQAP) ideologue Anwar al-Awlaki and the group’s propaganda outlet Inspire magazine (e.g. aforementioned Roshonara Choudry and Jose Pimentel, a Dominican American jihadist involved in a New York bomb plot during 2011).


Repression and Counter-terrorism

An alternative or supplementary explanation offered is state repression and counter-terrorism. It is important to bear in mind that ideological and strategic thinking on leaderless resistance emerged as responses to intensified crackdowns or disruption of extremist movements and terrorist groups; in particular the U.S. government’s crackdown of the white supremacy movement and the targeting of Al-Qaeda’s central organisation in the Af-Pak region and other Al-Qaeda strongholds - especially the increased use of drones against training camps and leading figures. Therefore, in terms of establishing causality one must ask what comes first, ideology and strategy, or tactical adaptation to a dire security environment. In this respect it is important to note that the afore-mentioned Al-Qaeda strategist Abu Musab al-Suri started writing about leaderless resistance in the 1990s, but that the popularization of his texts and the increase in individual jihadist attacks emerged only after Al-Qaeda came under severe pressures. As mentioned, a similar dynamic was seen among American white racists.

Psychological and societal factors

Besides ideology and adjustment to counter-terrorism regimes, other explanatory models emphasize psychological and societal factors. Whereas, generally, terrorists tend to be psychologically normal (Crenshaw 1981), mental difficulties seem to be over-represented among single actors.[28] Spaaij found lone wolves to have “greater propensity to suffer mental health issues”, and I found most jihadist loners to be either mentally or socially troubled, or both.[29] Another important observation by Spaaij is that lone wolves tend to mix personal frustrations and extremist ideologies, externalizing their own problems, blaming them on the hostile “Other,” be it immigrants, multiculturalism, or the Jewish-Crusader imperialist alliance.

Broader societal tendencies towards individualization and social fragmentation and alienation may intensify such radicalisation processes. Alienated and socially isolated persons could drift into a world of online extremism and violent computer games, and in rare instances they could end up being exploited by terrorist organisations, or radicalise and embark on violent rampage on their own, a case in point being school massacres. However, while there have been observed similarities between perpetrators of school massacres and terrorists[30], and while there is evidence that many lone terrorists have radicalised online, explanations emphasizing the Internet and social changes do not account for historical patterns of single actor terrorism (such as the 19th century anarchists). In addition, the fact that most single actor terrorists had, or wanted to have ties to group environments largely invalidates individualism as a driver in its own right.


Tactical Diffusion/Contagion

A more general explanation for terrorist violence is the effect of contagion (Midlarsky et al 1980; Schmid & de Graaf 1982).[31] Terrorism research has solidly documented that terrorists tend to emulate each other’s operational methods. Globalisation and Internet-based mass media and social media accelerate and intensify such processes (Nacos 2009).[32]

It was the Lebanese Shia-militia Hizbullah that introduced suicide bombings that later were employed by Palestinian terrorists, Tamil Tigers and Al-Qaeda; IED expertise from Iraq spread to other theaters of war and insurgency, and the Dutch-Moroccan jihadist Mohammed Bouyeri killed and tried to decapitate filmmaker Theo Van Gogh on the streets of Amsterdam, shortly after a kidnapping and decapitation campaign executed by Al-Qaeda in Iraq during 2004.

The Norwegian terrorist Anders Behring Breivik explained in detail how he gained tactical inspiration from Al-Qaeda when aiming to launch a martyrdom solo terrorist attack in Oslo, and now security services worry that other terrorists in turn could learn from Breivik. While both strategic-tactical considerations and socio-psychological factors apparently influence the occurrence single actor terrorism, in the Internet age it is important not to underestimate the contagious nature of extreme violence, and the potential for spread among terrorist networks and copycat killers.



Existing research indicates that single actor terrorism is a marginal phenomenon and less dangerous than group terrorism. However, worldwide attacks over the last couple of years suggest that single actor terrorism is on the rise and becoming more deadly. Available studies of terrorist attacks by individual perpetrators suffer from a lack of coherent definitions and sound operationalizations, while utilizing poor data.  Although studies have produced well-founded knowledge about single cases or clusters of cases, there are serious questions regarding the validity of findings and generalization. Because the research does not distinguish accurately between lone terrorists and network agents it is difficult to know when and how we may perceive single actor terrorist attacks as a distinct phenomenon or as a tactical variant of group terrorism.

At the end of the day it is crucial to make this distinction in order to understand variations in the occurrence of individual terrorist attacks. Do single actor attacks occur when terrorist groups face troubles and adapt their tactics, or do broader societal changes account for a recent increase in this type of terrorism, or both? A main challenge ahead for the research community is to operationalize connections and affinity between a lone attacker, networks and ideological communities. How much and what types of contacts between a lone attacker and a broader social entity is needed to distinguish between political terrorists and lunatic killers?

Also, how ‘political’ must a violent attacker be to qualify as a single actor terrorist? When social grievances and psychological problems overshadow political messages there is indeed a fine line between terroristic violence and other types of random violence, such as school massacres.

Several studies of single actor terrorism are currently in the pipeline. Hopefully they will rely on more complete and accurate data than is currently available. For example, recent observations concerning the scope and lethality of the phenomenon could be altered substantially if well-documented thwarted and failed terrorist attacks were included in the databases. Also there is a need for cross-comparison between single actor attacks within different ideological camps. Closer investigations could, for example, reveal important differences between actors, methods and motivational drivers within the right-wing, jihadist or anarchist realms. Despite data problems and analytical pitfalls, what seems to be a robust finding in the existing research is that single actor terrorism appeals to a special kind of person - people of unusual psychological complexity.

Another feature worth noticing is the relatively low lethality in Spaaij’s historical data material. Moreover, my survey of jihadist loner attacks in Europe showed a low success rate in terms of destruction and fatalities, indicating that single actors face substantial operational challenges compared to groups and that they tend to make mistakes. However, the terrorist attacks in Oslo, the shootings at Fort Hood and Mohammed Merah’s terrorist campaign in France constitute a worrisome trend of successful attacks, which could be linked to contagion and diffusion of tactical advice via Internet outlets and social media. The recent massacres in America, the Batman shootings by a schizophrenic madman and the Nazi attack on a Sikh-temple further demonstrated the operational effectiveness of lone attackers armed with handguns.

About the Author: Petter Nesser (M.A., PhD) is a Senior Research Fellow with the Norwegian Defence Research Establishment (FFI). He is trained in the areas of Social Science, Middle Eastern Studies and Arabic. Nesser’s specialisation is within the field of Islamist militancy and terrorist networks in Western Europe. He currently heads FFI's Terrorism Research Group.



[1]Ramon Spaaij, Understanding Lone Wolf Terrorism (Melbourne: Springer, 2012); Jeffrey Kaplan, "Leaderless resistance," Terrorism and Political Violence, 9:3, 80-95; Center for Terroranalyse (CTA) "The threat from solo terrorism and lone wolf terrorism," 5 April, 2011, URL:

[2] George Woodcock, Anarchism: A History of Libertarian Ideas and Movements. Cleveland & New York: Meridian Books, 1962.

[3] See e.g. COT - Instituut voor Veiligheids- en Crisismanagement ,“Lone Wolf Terrorism,” Report, The Hague: COT, 6 July 2007 and Martin Durham, White Rage. New York: Routledge, 2007.

[4] Louis Beam, ”Leaderless Resistance,” The Seditionist, Issue 12, February 1992, URL:

[5] Andrew McDonald “The Turner Diaries,” 1978; ------, “Hunter,” 1989, accessed via JR’s Rare Books and Commentary, URL:

[6] Tom Metzger, "Begin With Lone Wolves," URL:

[7] Brynjar Lia, Architect of Global Jihad: The Life of Al-Qaeda Strategist Abu Mus’ab Al-Suri . New York: Columbia University Press, 2007.

[8] Ibid.

[9] Inspire magazine is available on a number of jihadist websites, and may also be accessed via the blog Jihadology, URL:

[10] Jeffrey Kaplan, “Leaderless Resistance“, Terrorism and Political Violence, Vol. 9, No. 3, pp. 80-95, 1997; Randy Borum, Psychology of Terrorism Tampa: University of South Florida, 2004; Marc Sageman, Leaderless Jihad: Terror Networks in the Twenty-First Century. Philadelphia: University of Pennsylvania Press, 2008.

[11] Ramón Spaaij, Understanding Lone Wolf Terrorism: Global Patterns, Motivations and Prevention.  Dortrecht: Springer, 2012, Edwin Bakker and Beatrice De Graaf, "Lone Wolves: How to Prevent This Phenomenon?," report, International Centre for Counter-Terrorism, November 2010; Rafaello Pantucci, “A Typology of Lone Wolves: Preliminary Analysis of Lone Islamist Terrorists”, report, International Center for the Study of Radicalisation (ICSR, 2011).

[12] He suggests a typology distinguishing between the loner (individual acting on his own inspired by ideology), the lone wolf (individual acting on his own inspired by ideology and linked to extremist networks), something he calls lone wolf pack (small group acting on its own inspired by ideology), and the lone attacker (individual dispatched by terrorist group); see Pantucci, “A Typology of Lone Wolves”.

[13] The 15 countries surveyed include UK, Germany, France, Spain, Italy, Poland, The Netherlands, Denmark, Sweden, Croatia, Portugal, Russia, Australia, Canada and the U.S.

[14] Cases include the “Una-bomber” Ted Kaczynski (operating between 1978 and 1995), Austrian xenophobic serial killer Franz Fuchs (operating between 1993 and 1997), Jewisk extremist Yigal Amir who killed Israeli Prime Minister Yitzhak Rabin in 1995, right-wing terrorist David Copeland who attacked foreigners and gay people in the UK during 1999 and the Dutch environmental extremist Volkert Van der Graaf who killed the liberal politician Pim Fortuyn in 2002.

[15] 45 % of the 198 attacks took place in the U.S.. Germany was the second most exposed country in the data material, having experienced eight lone wolf attacks in the period surveyed.

[16] Remaining categories include black militancy terrorism, left-wing terrorism, Eco-terrorism, animal liberation terrorism, Spaaij (2012).

[17] See for example Jan Oskar Engene’s study, Terrorism In Western Europe: Explaining The Trends Since 1950. Cheltenham: Edward Elgar Publishing, 2004; he shows that separatists have been behind the vast majority of terrorist attacks in European countries since World War II. See also statistics presented in Brynjar Lia with Katja Skjølberg, "Causes of terrorism: An Expanded and Updated Review of the Literature," FFI Research Report No.2004/04307, p 14, URL: , showing a similar tendency based on RAND-MIPT terrorism incident data.

[18] For example, Franz Fuchs’ racism and xenophobia seemed to involve considerable levels of self-hate and Yigal Amir’s radicalisation process appeared to accelerate in connection with a broken relationship with his girlfriend.

[19] For example, only one out of the archetypical lone wolves studied by Spaaij was in a relationship.

[20] For a preliminary analysis, see Petter Nesser, Petter Nesser, "Individual Jihadist Operations in Europe: Patterns and Challenges," CTC Sentinel, Vol. 5, Issue 1, January 2012, URL: For the purpose of the current analysis several additional cases were included, see full list in body text.

[21] Petter Nesser, "Chronology of Jihadism in Western Europe 1994-2007: Planned, Prepared, and Executed Terrorist Attacks" Studies in Conflict & Terrorism, Vol. 31, No. 10 (2008), and Nesser "Chronology of Jihadism in Western Europe Update 2008-2010," FFI (2010), available on URL: and further updates for 2011 and 2012 with author.

[22] These cases included: the Kosovar Arid Uka who killed two U.S. soldiers and wounded two others at Frankfurt airport in 2011; the Pakistani female student Roshonara Choudry who stabbed a British MP during 2010; an Iraqi behind toxic letter attacks in Belgium during 2003 (see e.g. BBC News, "Belgium holds Iraqi over toxic letters," 5 June 2003, URL: ), and the mentally unstable Dutch-British jihadist “wannabe” Nicholas Roddis, who gathered bomb-materials and staged a bomb hoax in the UK during 2008. The circumstances of all these cases were vague, but clear links to well-known networks seem to be absent - at least to this author’s knowledge.

[23] The three cases that preceded 2008 included: “shoe-bomber” Richard Reid, Mohammed Bouyeri, who killed the Dutch filmmaker Theo Van Gogh, - and the toxic letters’ case in Belgium.

[24] Attacks on soft military targets included: Arid Uka’s shooting of U.S. soldiers in Frankfurt, the Libyan Mohammed Game’s explosives attack at the gate of a U.S. military base in Milan, and Mohammed Merah’s assaults on French soldiers before attacking a Jewish school.

[25] Young Nicky Reilly who tried to bomb a restaurant in Exeter suffered from Asperger and “Emo-kid” Andrew Ibrahim who planned to bomb a shopping center in Bristol struggled with behavioral transgressions, as did Theo Van Gogh’s murderer Mohammed Bouyeri. 23-year-old Nicholas Roddis who was fascinated with jihadism and staged a bomb-hoax in Britain also suffered from mental problems.

[26] Albert Benschop, “Chronicle of a Political Murder Foretold: Jihad in the Netherlands,” online report, University of Amsterdam, 2005.

[27] Such as Tom Metzger’s call for “Lone Wolfism” in "Begin With Lone Wolves," URL:

[28] Martha Crenshaw, “The Causes of Terrorism.” Comparative Politics, Vol. 13, no. 4, pp. 379-399, 1981.

[29] Ramón Spaaij (2012), p 50.

[30] Adam Lankford and Nayab Hakimb, "From Columbine to Palestine: A comparative analysis of rampage shooters in the United States and volunteer suicide bombers in the Middle East," Aggression and Violent Behavior, Volume 16, Issue 2, March–April 2011, pp. 98–107.

[31] Midlarsky et al, "Why Violence Spreads," International Studies Quarterly, Vol. 24, No. 2 (Jun., 1980), pp. 262-298; Alex P. Schmid and Janny de Graaf. Violence and Communication: Insurgent Terrorism and the Western News Media London: Sage, 1982.

[32] Brigitte L Nacos, "Revisiting the Contagion Hypothesis: Terrorism, News Coverage, and Copycat Attacks," Perspectives on Terrorism, Vol 3, No 3 (2009), URL: ; Alex P. Schmid and Janny de Graaf, op. cit.

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