Revisiting the Contagion Hypothesis: Terrorism, News Coverage, and Copycat Attacks

Revisiting the Contagion Hypothesis: Terrorism, News Coverage, and Copycat Attacks

by Brigitte L Nacos


Contagion refers here to a form of copycat crime, whereby violence-prone individuals and groups imitate forms of (political) violence attractive to them, based on examples usually popularized by mass media. In the late 1960s and early 1970s, for instance, Palestinian terrorists staged a number of spectacular hijackings of commercial airliners, exploited the often prolonged hostage situations to win massive news coverage for their political grievances, and appeared to inspire other groups to follow their example. Although terrorism scholars, government officials, and journalists have pondered the question of mass-mediated contagion for decades, they have arrived at different conclusions. Because of significant advances in communication and information technology, and changes in the global media landscape during the last decade or so, this article reconsiders arguments surrounding contagion theories and contends that various types of media are indeed important carriers of the virus of hate and political violence.



On April 19th, 1995, Timothy McVeigh ignited a homemade truck bomb that destroyed the Alfred P. Murrah Federal Building in downtown Oklahoma City, killing 168 persons, injuring close to 700 more, and triggering massive news coverage at home and abroad. Five days later, the director of the California Forest Association, Gilbert Murray, was killed instantly when he opened a small package that had been mailed to his office. The enclosed message revealed that the sender was the mysterious person dubbed "Unabomber" by the FBI; he had killed already two other people and injured 23 via mail bombs since 1978. That same day, The New York Times received a letter from the Unabomber threatening another deadly parcel bomb mailing unless the newspaper published a 35,000 words manifesto he had written to explain his motives. It is difficult to imagine that there was no link between the non-stop coverage of the terrorist spectacular in Oklahoma City and the timing of the simultaneous mailings to Murray's office and the Times. My guess was then and is now that the Unabomber, Theodore Kaczynski, was miffed because of the relatively modest news coverage his mail bombs had received over the years compared to the tremendous attention the mass media paid to the Oklahoma City bombing. More importantly, whereas McVeigh's grievances and motives were prominently covered since he had intentionally posited clues in his car (i.e., Waco, Ruby Ridge), there had been no definitive news about the Unabomber's motives in the wake of his long mail bombing trail.

Thus, Kaczynski wasted no time to finally get his share of media attention and recognition of his cause by sending off another mail bomb and a threatening letter to the country's leading newspaper. By September 1995, when The Washington Post also published his full-length manifesto "Industrial Society and Its Future" - sharing the printing costs with The New York Times - the Unabomber had already overtaken McVeigh as terrorist newsmaker-in-chief, seeing finally his grievances widely publicized and discussed in the mass media. It can be plausibly argued that the deadly mail bomb, the letter to the Times, a follow-up threat to bomb the Los Angeles airport contained in a letter to the San Francisco Chronicle and a host of demands and threats communicated to several newspapers and magazines were indeed inspired by the high volume and nature of news coverage about the Oklahoma City bombing in order to get comparable coverage. However, it is, in this case, impossible to prove media-related contagion unless the imprisoned perpetrator, Kaczynski, himself were to confirm such a contagion effect. While this case speaks to the difficulty of finding conclusive evidence for direct media-induced contagion with respect to terrorist acts, it encourages the exploration of media coverage of terrorist incidents, methods, and, most importantly, ideologies as a vector of terrorist infection. In the following, I revisit the media contagion hypothesis as it relates to terrorism and, to a lesser extent, for comparative purposes, to violence-as-crime.

Contagion Theories

Contagion theories have been forwarded and rejected with respect to terrorism for several decades—often in the context of media effects. While some scholars deny such a cause-effect relationship,[1] the notion of mass-mediated contagion seems commonsensical and is indeed supported by anecdotal accounts as well as more systematic research.[2]

However, more than twenty years ago Robert G. Picard attacked the news-as-contagion theory as "backed by dubious science" and argued, "[t]he literature implicating the media as responsible for the contagion of terrorist violence has grown rapidly, but, under scrutiny, it appears to contain no credible supporting evidence and fails to establish a cause-effect relationship."[3] He cited the minimal press effect findings of social scientists in the 1940s and 1950s in support of his rejection of the media contagion theory.[4] What he failed to mention was that ample and far from "dubious" research conducted since the 1960s which found far stronger media effects on audiences (most notably with respect to agenda setting, framing, and priming) than the minimal effect school.

Writing with Northern Ireland and domestic UK terrorism in mind, Schlesinger, Murdock, and Elliott, too, rejected the idea that the media are spreading the virus of political violence, claiming that it ignored the intelligence and good judgment of news consumers and especially television audiences.[5]

However, based on their quantitative analysis of media reporting (or non-reporting) of terrorist incidents and subsequent terrorist strikes of the same type (i.e., hijackings, kidnappings), Gabriel Weimann and Conrad Winn concluded that their data "yielded considerable evidence of a contagion effect wrought by coverage." More specifically, these scholars found that "television coverage was associated with a shortened lag time to emulation in the case of kidnapping, attacks on installations, hijackings, bombings, and assassinations."[6]

Alex P. Schmid and Janny de Graaf concluded in their study Violence as Communication that "[t]he media can provide the potential terrorist with all the ingredients that are necessary to engage in this type of violence. They can reduce inhibitions against the use of violence, they can offer models and know-how to potential terrorists and they can motivate them in various ways."[7] Similarly, Brian Jenkins wrote, "Initial research tentatively suggests that heavy media coverage of hijackings, kidnappings and other hostile seizures carried out by terrorists increases the likelihood that similar incidents will occur in the period immediately following. A RAND analysis of embassy seizures during the 1970s showed them occurring in clusters, clearly suggesting a contagion effect."[8]

Assumptions or inferences about contagion in the area of violent crimes are often based on observations and statistical data in the context of particularly horrific incidents. For example, Berkowitz and Macaulay studied crime statistics in the aftermath of the assassination of President John F. Kennedy in 1963 and subsequent to two mass killings in 1966, when Richard Speck killed eight nurses in Chicago and Charles Whitman shot 45 persons from a tower at the University of Texas. The researchers found that "[s]tatistical and graphic data from 40 U.S. cities indicate" that those incidents "were followed by unusual increases in the number of violent crimes."[9] While the scholars characterized theses cases as "widely published crimes" and implied a relationship between heavy news coverage of the three incidents and subsequent jumps in the number of violent crimes, they did not argue that most such crimes are instigated by media reports."[10]

More recently, Loren Coleman explored the links between the Columbine school shooting in 1999 (when high school students Eric Harris and Dylan Klebold killed 12 and injured 23 fellow students) and some 400 similar incidents in the following years, including the Virginia Tech campus shooting in 2007, when student Seung-Hui Cho killed 32 people and wounded many others. In many of these cases the killers revealed the copy-cat nature of their violence by referring directly or indirectly to the Columbine massacre. In Coleman's words, "The copycat effect is what happens when the media makes an event into a 'hot death story" and then via behaviour contagion, more deaths, suicides, murders, and more occur in a regularly predictive cycle…."[11]

But just as the media-terrorism connection is embraced or contested by communication-, media-, and terrorism- scholars, there is also disagreement about the impact of media reporting on violent crimes. In a comprehensive, recent review of the relevant literature, one expert in the field cautioned:

"Despite the vast volume of published literature that has concluded that the causal link between media violence and antisocial behaviour is established, there have been more cautious and even dissenting voices that have challenged the strong effects position. Some writers have accepted that media violence can influence viewers, but not all the time and not always to the same degree in respect of different members of the audience."[12]

As for mass-mediated diffusion of terrorism, the strongest arguments against connections between media content and terrorist incidents are made by those who fear that the notion of the media as agent of terrorist contagion will strengthen the hands of governments in efforts to curb or alter terrorism-related content and thereby interfere with freedom of the press and freedom of expression. I share those concerns and oppose censorship categorically. Yet these concerns must not prevent us from considering possible connections between media content and terrorism contagion and search for mitigating factors without media restrictions from government or other outside bodies.

Observations and Testimony

What is perhaps the most-cited example for media-related contagion of violence or the threat thereof is the case of D.B. Cooper. In November 1971 he hijacked a commercial airliner on the flight from Portland to Seattle under the threat of detonating a bomb in his briefcase. After receiving a $200,000 ransom and two parachutes at the Seattle-Tacoma Airport and ordering the crew to fly at the lowest possible altitude to Las Vegas, he jumped out of the plane - never to be seen again. In the wake of heavy media coverage and the release of songs and a motion picture devoted to his daredevil heist, Cooper became a cult hero. More importantly, he inspired a series of more than two dozen copycat hijackings by other criminals during which the hijackers also asked for ransom money and parachutes along the lines of Cooper's deed.[13]

As for political terrorism, some of the best evidence of contagious media content comes from the testimony of captured terrorists or ex-terrorists themselves. According to two scholars, "Horst Mahler, one of the founders of the German Red Army Faction [RAF], recalled years later how television newscasts had triggered the 'shock…[which led to] self-liberation…[and] the basis for RAF ideology. Several biographical studies of terrorists show that many were motivated by a desire to emulate the publicity achievements of precursors."[14] Another example is that of South Moluccan nationalists who hijacked trains in the Netherlands on two occasions in the 1970s to dramatize the Indonesian occupation of their fathers' homeland, the South Moluccas. They reportedly admitted after their arrest that their deeds were inspired by a similar attack plotted by Arab terrorists en route to Austria."[15]

Copycatting Terrorist Methods/Tactics of Attack

In the case of the South Moluccan train hijackers, media reports affected simply what method of attack the group would selected as most likely to succeed from what one would assume were several options the extremists considered. This appears to be a quite common media-related contagion effect that explains why particular modes of terrorist attacks tend to come in clusters or waves. Thus, beginning with the hijacking of commercial airliners by Palestinian terrorists in the late 1960s (who, in turn, were probably inspired by a wave of hijackings from and to Cuba), other Palestinian and non-Palestinian groups followed suit so that there was a cluster of hijackings with passengers held hostage. This method remained attractive into the 1970s and beyond. Yet as airlines and governments improved their security systems, the takeover of planes became more risky. While terrorists continued to hijack planes and in the case of the "Achille Lauro" even a cruise ship, it was no longer the preferred method of attack. Instead, terrorist groups embraced other means of attacking different targets and victims, e.g., embassy takeovers.

Based on incident data collected by the RAND Corporation, Brian Jenkins found that 43 successful embassy takeovers and five unsuccessful attempts occurred between 1971 and 1980 in 27 countries, targeting the embassies of many countries—albeit most of all those of the United States and Egypt. "Like many other tactics of terrorism, hostage-taking [in embassies] appears to be contagious," Jenkins concluded. "The incidents do not fall randomly throughout the decade, but occur in clusters."[16] It is plausible to argue that one event inspired the next, especially if successful. Presumably, terrorists learned about these takeovers, most of them successful, from media reports since these incidents took place in a host of different countries on different continents. By late 1979, when the Iran Hostage Crisis began, the "students" who took over the U.S. embassy in Teheran and the Iranian leaders who backed them must have known (via news accounts) about the prominent news coverage such incidents received. After all, of the embassy takeovers during the 1970s, more than half occurred in the last two years of the decade.

Or take as a more recent example the cluster of gruesome beheadings of American, British, Japanese, and South Korean hostages by ruthless terrorists in Iraq and other countries in the region, starting in the spring of 2004 with the killing of Nicholas Berg, a Philadelphia businessman. Emotionally wrenching videotapes that depicted the hostages begging for their lives were posted on the Internet by the killers and were subsequently reported on by traditional news organizations' in shocking detail. Consider, for example, the following description of an American civilian's decapitation by his terrorist kidnappers as published in a leading U.S. newspaper:

As the insurgent speaks, the gray-bearded man identified as Mr.Armstrong appears to be sobbing, a white blindfold wrapped around his eyes. He is wearing an orange jumpsuit. The masked man then pulls a knife, grabs his head and begins slicing through the neck. The killer places the head atop the body before the video cuts to a shot of him holding up the head and a third, more grainy shot showed the body from a different angle.[17]

It is likely that the global wave of shock and outrage ignited by Berg's beheading inspired the decapitation of other hostages as a novel method of spreading terror from the Middle East. Indeed, there were a number of cases in which terrorists beheaded their victims or threatened to do so outside the Middle East. In Haiti, for example, the bodies of three headless policemen were found; they were victims of local terrorists who called their action "Operation Baghdad"—a label that had no previous meaning in Haiti's civil strife, except for the cruel method of murder copied from in Iraq. In another case of imitation, the beheading of a Buddhist official in a village in Thailand was described as an act of revenge for violence against Muslim rioters. After the shooting of the critical Dutch filmmaker Theo van Gogh (his killer tried to cut his throat as well), self-proclaimed jihadis in the Netherlands threatened to decapitate other critics of Muslim extremists. All of these perpetrators had recognized the shock-value and media attractiveness of this particularly gruesome terrorist tactic first performed for public consumption in Iraq.

As one terrorism expert concluded in this context, "[t]here is no doubt that besides direct contacts between terrorist groups and/or individual terrorists, indirect observations of successful terrorist methods and strategies rely on traditional news reports and, more recently, new media outlets—especially Internet sites."[18] Examining the diffusion of suicide terrorism, Mia Bloom explained:

We can discern the direct (patron-client) and indirect (through observation) influences of suicide terror. In some instances, insurgent factions have been physically trained by other organizations and taught how to best use horrifying tactics to devastating effect, who subsequently import the tactic far and wide…. On other occasions, factions observe the successful operations of groups from afar—because of the publicity and media attention engendered by spectacular bombings, and then tailored the techniques to suit local circumstances.[19]

While suicide terrorism spread inside and outside the Middle East well before 9/11, it became an even more popular weapon since 9/11. Examining possible reasons for the post-9/11 wave of suicide terrorism, Paul Marsen and Sharon Attia argued that the media cannot cause "suicide bombings any more than sex (as opposed to HIV) can cause AIDS", but they also suggested that media might be "a vector of transmission that can precipitate its spread."[20] Considering the publicity success of the 9/11 attacks from the perspective of Al Qaeda and the organization's supporters and sympathizers, in an article published in 2003 I pointed to the likelihood of spectacular homicide-suicide attacks becoming a most-attractive model for future acts of terrorism in one form or the other.[21] While nobody has repeated the flying-of-commercial-airliners-into-buildings scenario on a similar scale so far, there have been many spectacular homicide-suicide attacks since 9/11 in different countries and continents.[22]

To summarize, besides personal contacts and cooperation between various groups, mass media reports are the most likely sources of information about the efficacy of terror methods and thus important factors in the diffusion of terrorist tactics. Interestingly, based on their analysis of terrorist incidents in the 1960s and 1970s around the globe, Midlarsky, Crenshaw and Yoshida concluded that some terrorist methods of attacks (hijackings, kidnappings, and bombings) were more contagious than others (assassinations, raids). These scholars recognized also that publicity provided by the news media was a factor in terrorists' decision to imitate terrorist methods deemed effective. As they put it, "Visible and unusual violence is in essence newsworthy and attracts international publicity necessary for cross-regional and cross-cultural spread."[23]

Inspirational Contagion

The adoption of effective terrorist tactics, however, does not cause terrorism per se because those tactics are imitated or adapted by organizations that already exist and have embraced terrorism. As one expert in the field put it:

A particular terrorist technique is only of interest to a group that has already made the decision to adopt a terrorist strategy; a technique cannot on its own cause a resort to terrorism. Similarly, a radical group will normally enter into direct contact with an established terrorist group only once the decision to adopt a terrorist strategy has already been made.[24]

Inspirational contagion is more alarming for the targets of terrorism because it is the stuff that makes terrorists tick and leads to the formation of new organizations and cells. The above-mentioned recollection of one of the Red Army Faction's founders, Horst Mahler, about the crucial role of televised terrorism news in formulating his group's ideology and the RAF's raison d'etre might not have been a surprise for Midlarsky, Crenshaw and Yoshida whose data analysis revealed the spread of terrorist thought from the Third World, and particularly from Latin-American and Palestinian terrorist leaders and groups, to Western Europe in the early 1970s. Noting that radicals in Germany and elsewhere in Western Europe received this sort of inspirational information from the mass media, the three scholars figured that "physical contacts [for example, between RAF and Palestinian groups] followed rather than preceded the decision to adopt terrorism."[25]

Writing more than a quarter century later and considering David Rapoport's categorization of four global waves of terrorism, Mark Sedgwick suggested

Contagion is possible at two levels, and can happen in two ways. On one level, a group might copy a particular terrorist technique, and on another level a group might copy a general terrorist strategy. Either of these might happen directly or indirectly. All these forms of contagion take place. The primary form, however, is the adoption of a general terrorist strategy without direct contact. All other forms of contagion are secondary to this.[26]

The most recent, most lethal, and geographically most diffused inspirational virus originated with Afghan mujahideen fighting Soviet occupiers in the 1980s and, most important, with the establishment of Al Qaeda and its rapidly expanding terrorism network. It is hardly surprising that contagion effects tend to be far stronger among those individuals and groups that share the cultural and religious background of organizations and leaders with inspirational ideologies. Whereas kinship and friendship brought the members of the Al Qaeda Central organization together,[27] the mighty 'Afghan wave'[28]that reached literally all continents in the post-9/11 years is now mostly driven by inspirational contagion.[29] As Marc Sageman noted:

The Islamist terror networks of the twenty-first century are becoming more fluid, independent, and unpredictable entities than their more structured forebears, who carried out the atrocities of 9/11. The present threat has evolved from a structured group of al Qaeda masterminds, controlling vast resources and issuing commands, to a multitude of informal local groups trying to emulate their predecessors by conceiving and executing operations from the bottom up. These 'homegrown' wannabes form a scattered global network, a leaderless jihad.[30]

In the first decade of the new millennium the Internet has become the agent of virtual inspirational contagion spread by a multitude of extremist web sites with chat rooms and message boards that condition and inspire especially vulnerable young men and, increasingly, women within the Muslim world and in the diaspora to form or join autonomous groups or cells and plot terrorist strikes.[31]

But other kinds of ideologies of hate and terror are also disseminated via old and new media and communication technologies. There can be little doubt that the inspirational virus is particularly potent when diffused through media forms that are not subject to checks by the traditional media gatekeepers. It is for this reason that inspirational contagion spreads faster and further via books, CDs, and, of course, the Internet.

Timothy McVeigh was inspired by the extremist anti-government and White Supremacy doctrines of the militia movement, neo-Nazi groups, and Christian Identity cells as these were synthesized by William Pierce, the founder of the neo-Nazi National Alliance. Using the pseudonym Andrew McDonald, Pierce published the novel The Turner Diaries that describes an all out race war—starting with the bombing of FBI headquarters in Washington. McVeigh and Pierce did not have any personal contact. Yet The Turner Diaries was the book that inspired McVeigh's extremist worldview and, at the same time, served him as a blueprint for the actual bombing plot. His accomplice Terry Nichols was inspired by another novel, "Hunter", authored by Pierce under the McDonald name that was just as racist and violent as The Turner Diaries.

Or take the extremist fringe in the anti-abortion movement that uses web sites to spread its hateful agenda in the name of God, displaying gruesome pictures of bloody fetuses of "butchered" children. They publicize the names and locations of abortion providers, celebrating the murderers of abortion providers as inspirational heroes and role models. They also cites from the bible to spread the word that God is on the side of those who serve as soldiers in the 'Baby Liberation Army'. After Dr. George Tiller, a physician who provided legal abortions in Wichita, Kansas, was shot in May 2009 during a Sunday morning service in his church by Scott Roeder, it was revealed that the killer had been a frequent visitor to several of the most notorious anti-abortion websites. On one occasion, he had posted a message on a fake web site that labeled Dr. Tiller "the concentration camp Mengele of our day" who "needs to be stopped before he and those who protect him bring judgement upon our nation."[32] It is likely that he took this comparison from the Army of God's and/or similar web sites that vilified Tiller by comparing him to Dr. Josef Mengele, a Nazi physician in the Auschwitz concentration camp. Not surprisingly, The Army of God praised Roeder's killing of "Tiller the Killer" on its web site and demanded that Roeder must be found not guilty" since he "faced a terrible evil…"[33]

In conclusion, when it comes to international and domestic terrorism, various kinds of media figure quite prominently in both tactical and inspirational contagion. While the Internet has moved center-stage in this respect during the last decade, the targets of terrorism have not been able to effectively counter the mass-mediated virus of this form of political violence. Recognizing this, U.S. Secretary of Defense Robert Gates said,

[P]ublic relations was invented in the United States, yet we are miserable at communicating to the rest of the world what we are about as a society and a culture, about freedom and democracy, about our policies and our goals. It is just plain embarrassing that al-Qaeda is better at communicating its message on the internet than America. As one foreign diplomat asked a couple of years ago, "How has one man in a cave managed to out-communicate the world's greatest communication society?"

Speed, agility, and cultural relevance are not terms that come readily to mind when discussing U.S. strategic communications.[34]

About the Author: Brigitte L. Nacos is a journalist and adjunct professor of political science at Columbia University. Besides other books and articles, she authored 'Terrorism and Counterterrorism: Understanding Threats and Responses in the Post-9/11 World'; 'Mass-Mediated Terrorism: The Central Role of the Media in Terrorism and Counterterrorism'; and 'Fueling Our Fears: Stereotyping, Media Coverage and Public Opinion of Muslim Americans'.


[1] Robert G. Picard, "News Coverage as the Contagion of Terrorism: Dangerous Charges Backed by Dubious Science." Paper presented at the Annual Meeting of the Association for Education in Journalism and Mass Communication at Norman, OK, August1986; Philip Schlesinger, Graham Murdock, and Philip Elliott, Televising Terrorism: Political Violence in Popular Culture. New York: Charles Scribner's Sons. 1984.

[2] Alex P. Schmid and Janny de Graaf. Violence and Communication: Insurgent Terrorism and the Western News Media. London: Sage, 1982; Gabriel Weimann and Conrad Winn. The Theater of Terror: Mass Media and International Terrorism. New York:Longman, 1994.

[3] Picard, op. cit.,, p. 1.

[4] Robert G. Picard, "News Coverage as the Contagion of Terrorism: Dangerous Charges Backed By Dubious Science." In A. Odasuo Alali and Kenoye Kelvin Eke (Eds). Media Coverage of Terrorism: Methods of Diffusion. Newbury Park: Sage Publications. 1991, pp. 55-56.

[5] Schlesinger, Murdock, and Elliott, op. cit.

[6] Weimann and Winn, op cit., p. 277.

[7] Schmid and De Graaf, op. cit. p. 142.

[8] Brian Jenkins, "The Psychological Implications of Media-Covered Terrorism." Paper issued by the Rand Corporation. St. Monica,RAND, June 1981, p. 6.

[9] Leonard Berkowitz and Jacqueline Macaulay, "The Contagion of Criminal Violence." Sociometry, 34 (2) (Jun. 1971), p. 238.

[10] Ibid, pp. 241, 260.

[11] Loren Coleman, "The Copycat Effect," blogspot. com, April 19, 2007, p. 1.

[12] Barrie Gunter, "Media Violence: Is There a Case for Causality?" American Behavioral Scientist 51 (8), (April 2008), p. 1063.

[13]For a detailed description of the subsequent 26 incidents and the one that inspired D.B. Cooper himself, see A. P. Schmid & J. de Graaf, op. cit., 1982, pp. 133-136.

[14] G. Weimann and C. Winn, op. cit., pp. 217, 218.

[15] Alex P. Schmid and Janny de Graaf, "Insurgent Terrorism and the Western News Media: An Exploratory Analysis with a Dutch Case Study." Leiden, Center for the Study of Social Conflicts, November 1980.

[16] Jenkins, op. cit., p. 7.

[17] Neil MacFarquhar, 'Acting on Threat, Saudi Group Kills Captive American.' New York Times, 19 June 2004, p. 1.

[18]M ark Sedgwick. 'Inspiration and the Origins of Global Waves of Terrorism.' Studies in Conflict & Terrorism, 30 (2) (February 2007), p. 102.

[19] Mia Bloom, Dying to Kill: The Allure of Suicide Terror. New York: Columbia University Press, 2005, p. 122.

[20] Paul Marsden and Sharon Attia, "A deadly contagion?" The Psychologist, 18 (3), March 2005, p. 153. .

[21] Brigitte L. Nacos, "The Calculus behind 9-11: A Model for Future Terrorism? Studies in Conflict & Terrorism, Vol. 26, No. 1, January/February 2003.

[22] However, the idea of imitating the 9/11 attacks has been discussed among terrorists. Thus, the Colombian FARC wanted to fly a plane into the presidential palace during President Alvaro Uribe's inauguration but was unable to find a pilot willing to dye for the cause—even though the organization offered to give the suicide pilot's family a $2 million reward. – Incidentally, there was what looked very much like a copycat suicide with a small plane taking place in Milan, Italy, when the pilot, crashed his plane in the Pirelli Tower on 18 April 2002.

[23] Manus I. Midlarsky, Martha Crenshaw and Fumihiko Yoshida, "Why Violence Spreads: The Contagion of International Terrorism." International Studies Quarterly Vol. 24, No. 2, June 1980, p. 279.

[24] Sedgwick, op. cit., p.102.

[25] Midlarsky, Crenshaw and Yoshida, op. cit., p. 282.

[26] Sedgwick,op. cit., p. 102.

[27] Marc Sageman, Understanding Terror Networks. Philadelphia: University of Pennsylvania Press, 2004.

[28] Mark Sedgwick. 'Inspiration and the Origins of Global Waves of Terrorism.' Studies in Conflict & Terrorism, Vol. 30, No. 2, February 2007, pp. 106-107.

[29] Sedgwick, op. cit., pp. 106-7.

[30] Mark Sageman, Leaderless Jihad. Philadelphia: University of Pennsylvania Press, 2008, p. vii.

[31] For the importance of the Internet in the spread of inspirational terrorism, see Gabriel Weimann, Terror on the Internet: The New Arena, the New Challenges. Washington, D.C.: United States Institute of Peace, 2006; Brigitte L. Nacos, Terrorism and Counterterrorism: Understanding Threats and Responses in the Post-9/11 World. 3rd Edition. New York: Longman Pearson, 2010, chapter 15; and M. Sageman, Leaderless Resistance, op. cit., chapter 6.

[32] "The Suspect at a Glance." The Washington Post, June 2, 2009, available at , accessed August 20, 2009.

[33] From the web site of The Army of God. , accessed August 14, 2009.

[34] The remarks were made during the Landon Lecture at Kansas State University, Nov. 26, 2007. The transcript of the speech is available at , accessed September 1, 2008.


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