What Effect does Ideological Extremism have on Mass Shootings? An Assessment of Motivational Inconsistencies, Risk Profiles, and Attack Behaviors

ABSTRACT

Much like other violent extremists, some mass shooters embrace inconsistent, mixed, or customized beliefs and attack for a combination of personal and ideological reasons. This makes it difficult to understand what effects ideology has on their behavior. To obtain empirical answers, we studied (1) the frequency of extreme ideological interests and motives among public mass shooters, (2) differences between perpetrators with and without extreme ideological interests, and (3) the degree of consistency between their ideologies and attack outcomes. Findings suggest that from 1966–2023, approximately one-quarter of public mass shooters in the United States had extreme ideological interests and roughly 70 percent of them were partially motivated by those extreme beliefs. Mass shooters with and without extremist interests showed similar rates of childhood trauma, mental health problems, suicidality, crisis, substance abuse, and criminal records, but ideological shooters were more likely to create legacy tokens, use semi-automatic or automatic rifles, kill strangers and non-white victims, and be copycats or role models. It appears extremism was sometimes a correlate and sometimes a cause of their behavior, with a clear effect on shaping some attacks. Nevertheless, inconsistencies were common, and many attackers did not target locations or victims that fit their ideological enemies.

KEYWORDS:

• Mass shootings
• ideology
• extremism
• terrorism
• victim selection

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

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2. Christopher Wray, “FBI Director Christopher Wray Testifies on January 6 Capitol Attack,” C-SPAN, March 2, 2021, https://www.c-span.org/video/?509033-1/fbi-director-christopher-wray-testifies-january-6-capitol-attack&live.

3. Christopher Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats,” C-SPAN, April 15, 2021, https://www.c-span.org/video/?510634-1/house-select-intelligence-committeehearing-global-threats&live.

4. Adam Lankford, “The Myth of Martyrdom: What Really Drives Suicide Bombers, Rampage Shooters, and Other Self-Destructive Killers,” Behavioral and Brain Sciences 37, no. 4 (2014): 351–62.

5. Scott Atran, Talking to the Enemy: Faith, Brotherhood, and the (Un)making of Terrorists (HarperCollins, 2010), 363.

6. For critiques of this logic, see: Donald Holbrook and John Horgan, “Terrorism and Ideology: Cracking the Nut,” Perspectives on Terrorism 13, no. 6 (2019): 2–15; Lankford, “The Myth of Martyrdom”; Justin E. C. Tetrault, “What’s Hate Got to Do with It? Right-Wing Movements and the Hate Stereotype,” Current Sociology 69, no. 1 (2021): 3–23.

7. Holbrook and Horgan, “Terrorism and Ideology”; James Khalil, John Horgan, and Martine Zeuthen, “The Attitudes-Behaviors Corrective (ABC) Model of Violent Extremism,” Terrorism and Political Violence 34, no. 3 (2022): 425–50; Lankford, “The Myth of Martyrdom.”

8. Economist/YouGov Poll, “Capitol Takeover Approval,” The Economist, YouGov, 2023, https://docs.cdn.yougov.com/pvpz4fi6ym/econTabReport.pdf.

9. ABC News/The Washington Post, “Trump Approval is Low but Steady; on Charlottesville, Lower Still,” ABC News, The Washington Post, August 21, 2017, https://www.langerresearch.com/wp-content/uploads/1190a1TrumpandCharlottesville.pdf.

10. Pew Research Center, “Muslim Americans: No Signs of Growth in Alienation or Support for Extremism,” August 30, 2011, https://www.pewresearch.org/politics/2011/08/30/muslim-americans-no-signs-of-growth-in-alienation-or-support-for-extremism/.

11. Federal Bureau of Investigation, Crime Data Explorer: Hate Crime (Federal Bureau of Investigation, 2023); National Threat Assessment Center, Mass Attacks in Public Spaces: 2016–2020 (U.S. Secret Service, Department of Homeland Security, 2023).

12. Jerrold M. Post, “Current Understanding of Terrorist Motivation and Psychology: Implications for a Differentiated Antiterrorist Policy,” Terrorism 13, no. 1 (1990): 65–71.

13. Central Intelligence Agency, 11 September: The Plot and the Plotters (National Security Archive, 2003).

14. Clark McCauley and Sophia Moskalenko, “Understanding Political Radicalization: The Two-Pyramids Model,” American Psychologist 72, no. 3 (2017): 205–16; Fathali M. Moghaddam, “The Staircase to Terrorism: A Psychological Exploration,” American Psychologist 60, no. 2 (2005): 161–9.

15. Holbrook and Horgan, “Terrorism and Ideology”; Khalil, Horgan, and Zeuthen, “The Attitudes-Behaviors Corrective (ABC) Model of Violent Extremism”; McCauley and Moskalenko, “Understanding Political Radicalization.”

16. Lorne L. Dawson, “Taking Terrorist Accounts of Their Motivations Seriously: An Exploration of the Hermeneutics of Suspicion,” Perspectives on Terrorism 13, no. 5 (2019): 74–89; Mohammed Hafez and Creighton Mullins, “The Radicalization Puzzle: A Theoretical Synthesis of Empirical Approaches to Homegrown Extremism,” Studies in Conflict and Terrorism 38, no. 11 (2015): 958–75; Holbrook and Horgan, “Terrorism and Ideology”; John Horgan, Terrorist Minds: The Psychology of Violent Extremism from Al Qaeda to the Far Right (Columbia University Press, 2023); Khalil, Horgan, and Zeuthen, “The Attitudes-Behaviors Corrective (ABC) Model of Violent Extremism”; Lankford, “The Myth of Martyrdom”; Peter R. Neumann, “The Trouble with Radicalization,” International Affairs 89, no. 4 (2013): 873–93.

17. Wray, “FBI Director Christopher Wray Testifies on January 6 Capitol Attack”; Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats.”

18. Holbrook and Horgan, “Terrorism and Ideology.”

19. Joel A. Capellan, Joseph Johnson, Jeremy R. Porter, and Christine Martin, “Disaggregating Mass Public Shootings: A Comparative Analysis of Disgruntled Employee, School, Ideologically Motivated, and Rampage Shooters,” Journal of Forensic Sciences 64, no. 3 (2019): 814–23; Jason R. Silva, “Ideologically Motivated Mass Shootings: A Crime Script Analysis of Far-right, Far-left, and Jihadist-inspired Attacks in the United States,” Journal of Policing, Intelligence and Counter Terrorism 18, no. 1 (2023): 1–23.

20. Ibid.

21. Joel A. Capellan and Jason R. Silva, “An Investigation of Mass Public Shooting Attacks Against Government Targets in the United States,” Studies in Conflict & Terrorism 44, no. 5 (2021): 387–409; Silva, “Ideologically Motivated Mass Shootings.”

22. Joel A. Capellan, “Lone Wolf Terrorist or Deranged Shooter? A Study of Ideological Active Shooter Events in the United States, 1970–2014,” Studies in Conflict & Terrorism 38, no. 6 (2015): 395–413; Adam Lankford, “A Comparative Analysis of Suicide Terrorists and Rampage, Workplace, and School Shooters in the United States from 1990 to 2010,” Homicide Studies 17, no. 3 (2013): 255–74; Adam Lankford and Nayab Hakim. “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 16, no. 2 (2011): 98–107.

23. Capellan et al., “Disaggregating Mass Public Shootings.”

24. Capellan, “Lone Wolf Terrorist or Deranged Shooter?”; John Horgan, Paul Gill, Noemie Bouhana, James Silver, and Emily Corner, Across the Universe? A Comparative Analysis of Violent Radicalization Across Three Offender Types with Implications for Criminal Justice Training and Education (National Institute of Justice, 2016); Jeffery R. Osborne and Joel A. Capellan, “Examining Active Shooter Events through the Rational Choice Perspective and Crime Script Analysis,” Security Journal 30, no. 3 (2017): 880–902; Adam Lankford, “A Comparative Analysis of Suicide Terrorists and Rampage, Workplace, and School Shooters in the United States from 1990 to 2010”; Lankford, “The Myth of Martyrdom”; Jason R. Silva, “Ideologically Motivated Mass Shootings”; Jason R. Silva and Joel A. Capellan, “A Comparative Analysis of Media Coverage of Mass Public Shootings: Examining Rampage, Disgruntled Employee, School, & Lone-Wolf Terrorist Shootings in the United States,” Criminal Justice Policy Review 30, no. 9 (2019): 1312–41; Ibid.

25. Anti-Defamation League, “Murder and Extremism in the United States in 2022,” February 22, 2023, https://www.adl.org/resources/report/murder-and-extremism-united-states-2022.

26. Anti-Defamation League, “Murder and Extremism in the United States in 2022.”

27. Adam Lankford, James Silver, and Jennifer Cox, “An Epidemiological Analysis of Public Mass Shooters and Active Shooters: Quantifying Key Differences between Perpetrators and the General Population, Homicide Offenders, and People who Die by Suicide,” Journal of Threat Assessment and Management 8, no. 4 (2021): 125–44.

28. Ibid.

29. Randy Borum, Psychology of Terrorism (University of South Florida, 2004); Holbrook and Horgan, “Terrorism and Ideology”; Khalil, Horgan, and Zeuthen, “The Attitudes-Behaviors Corrective (ABC) Model of Violent Extremism”; Peter Langman, “Irrational Rationales: Vicarious and Fictional Justifications Among Ideological Killers,” International Journal of Comparative and Applied Criminal Justice 48, no. 2 (2024): 159–77; Lankford, “The Myth of Martyrdom”; Post, “Current Understanding of Terrorist Motivation and Psychology.”

30. See note 17 above.

31. Lewys Brace, Stephane J. Baele, and Debbie Ging, “Where Do ‘Mixed, Unclear, and Unstable’ Ideologies Come From? A Data-Driven Answer Centered on the Incelosphere,” Journal of Policing, Intelligence and Counter Terrorism 19, no. 2 (2024): 103–24; Daveed Gartenstein-Ross and Madeleine Blackman, “Fluidity of the Fringes: Prior Extremist Involvement as a Radicalization Pathway,” Studies in Conflict & Terrorism 45, no. 7 (2022): 555–78; Joint Counterterrorism Assessment Team, Mixing Ideologies Requires Multipronged Terrorism Prevention Efforts (The National Counter Terrorism Center, Department of Homeland Security, and Federal Bureau of Investigation, 2023); Daniel Koehler, “Switching Sides: Exploring Violent Extremist Intergroup Migration Across Hostile Ideologies,” Political Psychology 41, no. 3 (2020): 499–515; Ashley A. Mattheis, Amarnath Amarasingam, Graham Macklin, and Marc-Andre Argentino, “The Allen, Texas, Attack: Ideological Fuzziness and the Contemporary Nature of Far-Right Violence,” CTC Sentinel 16, no. 6 (2023): 16–22; Alexander Meleagrou-Hitchens and Moustafa Ayad, The Age of Incoherence? Understanding Mixed and Unclear Ideology Extremism (National Counterterrorism Innovation, Technology, and Education Center, 2023); Wray, “FBI Director Christopher Wray Testifies on January 6 Capitol Attack”; Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats.”

32. Daveed Gartenstein-Ross, Andrew Zammit, Emelie Chace-Donahue, and Madison Urban, “Composite Violent Extremism: Conceptualizing Attackers Who Increasingly Challenge Traditional Categories of Terrorism,” Studies in Conflict & Terrorism (2023): 1–27.

33. Ibid.

34. An exception is Brace et al., which employed a broader approach to studying mixed ideologies in online communities. Brace, Baele, and Ging, “Where Do ‘Mixed, Unclear, and Unstable’ Ideologies Come From?”

35. Rick Anderson, “The Bitter Life and Sudden Death of A.C.,” Seattle Weekly, April 20, 2017, https://www.seattleweekly.com/news/the-bitter-life-and-sudden-death-of-arcan-cetin/; Adam Taylor, “O. M. May Not Have Understood the Difference Between ISIS, Al-Qaeda and Hezbollah,” The Washington Post, June 13, 2016, https://tinyurl.com/yxf9p5vh.

36. Brace, Baele, and Ging, “Where Do ‘Mixed, Unclear, and Unstable’ Ideologies Come From?”; Gartenstein-Ross and Blackman, “Fluidity of the Fringes”; Joint Counterterrorism Assessment Team, Mixing Ideologies Requires Multipronged Terrorism Prevention Efforts; Meleagrou-Hitchens and Ayad, The Age of Incoherence?; Wray, “FBI Director Christopher Wray Testifies on January 6 Capitol Attack.”

37. Brace, Baele, and Ging, “Where Do ‘Mixed, Unclear, and Unstable’ Ideologies Come From?”; Mattheis et al., “The Allen, Texas, Attack.”

38. Meleagrou-Hitchens and Ayad, The Age of Incoherence?

39. Gartenstein-Ross and Blackman, “Fluidity of the Fringes”; Joint Counterterrorism Assessment Team, Mixing Ideologies Requires Multipronged Terrorism Prevention Efforts; Meleagrou-Hitchens and Ayad, The Age of Incoherence?

40. Joint Counterterrorism Assessment Team, Mixing Ideologies Requires Multipronged Terrorism Prevention Efforts.

41. Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats.”

42. Jason R. Silva and Adam Lankford, “The Globalization of American Mass Shootings? An Assessment of Fame-Seeking Perpetrators and Their Influence Worldwide,” International Journal of Comparative and Applied Criminal Justice 48, no. 2 (2024): 119–42.

43. Anti-Defamation League, Murder and Extremism in the United States in 2022.

44. Jillian Peterson and James Densley, “The Violence Project Database of Mass Shootings in the United States, 1966–2021 (Version 7),” The Violence Project, 2023.

45. William J. Krouse and Daniel J. Richardson, Mass Murder with Firearms: Incidents and Victims, 1999–2013 (Congressional Research Service, 2015), 10.

46. Grant Duwe, “Patterns and Prevalence of Lethal Mass Violence,” Criminology & Public Policy 19, no. 1 (2020): 17–35; Krouse and Richardson, Mass Murder with Firearms; Peterson and Densley, “The Violence Project Database of Mass Shootings in the United States.”

47. For example: Capellan, “Lone Wolf Terrorist or Deranged Shooter?”; Capellan et al., “Disaggregating Mass Public Shootings.”

48. Krouse and Richardson, Mass Murder with Firearms; Jason R. Silva, “A Comprehensive Study of Public, Family, and Felony Mass Shootings in the United States, 2006–2020,” Violence and Victims 37, no. 6 (2022): 717–38; Jaclyn Schildkraut and Adam Lankford, “Mass Shootings in the United States and Beyond: Definitions, Contexts, and Controversies,” in Routledge Handbook of Homicide Studies, ed. Katelyn Burgason and Matt DeLisi (Routledge, 2024), 140–65.

49. Lin Huff‐Corzine and Jay Corzine, “The Devil’s in the Details: Measuring Mass Violence,” Criminology & Public Policy 19, no. 1 (2020): 317–33. William S. Parkin and Jeff Gruenewald, “Open-Source Data and the Study of Homicide,” Journal of Interpersonal Violence 32, no. 18 (2017): 2693–723.

50. Grant Duwe, “Body Count Journalism,” Homicide Studies 4, no. 4 (2000): 364–99; Silva and Capellan, “A Comparative Analysis of Media Coverage of Mass Public Shootings.”

51. Adam Lankford, Krista Grace Adkins, and Eric Madfis, “Are the Deadliest Mass Shootings Preventable? An Assessment of Leakage, Information Reported to Law Enforcement, and Firearms Acquisition Prior to Attacks in the United States,” Journal of Contemporary Criminal Justice 35, no. 3 (2019): 315–41.

52. Mass shooters attacked by themselves in more than 95 percent of cases, but in rare cases involving dual perpetrators, we considered each shooter responsible for all victims harmed (as they would be in a court of law), rather than dividing the number of victims among the shooters.

53. In rare cases where we found an error, we updated the data with information from other research or reliable sources.

54. As we discuss in our “Limitations” section, beyond binary coding of extreme ideologies (1= yes, 0 = no evidence), several more complex options exist that could be pursued in future research.

55. See for example: Gartenstein-Ross et al., “Composite Violent Extremism.”

56. Coding a perpetrator as being ideologically motivated only meant the attack was partially motivated by that factor; attacks can involve multiple motives simultaneously (e.g., ideology, revenge, fame-seeking, and more).

57. First, although it is clear the 1991 Luby’s cafeteria shooter expressed anger against women, we could not find any evidence of extreme ideologies in his written or verbal statements or the investigation into his attack. Second, the police investigation of the 2017 Las Vegas shooting reported no evidence of extreme ideological interests, and the Federal Bureau of Investigation concluded that they “found no evidence that P.’s attack was motivated by any ideological or political beliefs.” Federal Bureau of Investigation, Key Findings of the Behavioral Analysis Unit’s Las Vegas Review Panel (LVRP) (Federal Bureau of Investigation, 2019); Las Vegas Metropolitan Police Department, LVMPD Criminal Investigative Report of the 1 October Mass Casualty Shooting (Las Vegas Metropolitan Police Department, 2018). Third, the only evidence linking 2018 Santa Fe shooter to extremism was a photo of him with an iron cross that some associate with Nazism, but he collected many pins from different cultures, specifically posted that he felt “Iron Cross = Bravery,” and made no direct references to Nazis or other forms of extremism that we could find. Finally, the 2021 Atlanta shooter targeted two spas and a massage parlor where most employees were Asian, but he explicitly told police his crimes were “not racially motivated” and that his anger against the establishments were based on his sexual problems. Elliot C. McLaughlin, Casey Tolan, and Amanda Watts, “What We Know about R. A. L., the Suspect in Atlanta Spa Shootings,” CNN, March 18, 2021, https://www.cnn.com/2021/03/17/us/robert-aaron-long-suspected-shooter/index.html. This seems credible given the “admissions against interest” standard, we found no evidence of extreme ideological interests, and at that point he had little to hide.

58. Silva and Lankford, “The Globalization of American Mass Shootings?”; Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats.”

59. Based on the recommendations from the “No Notoriety” campaign and Lankford and Madfis’s proposal to deny offenders the attention they often seek, we are not publishing mass shooters’ names. Adam Lankford and Eric Madfis, “Don’t Name Them, Don’t Show Them, but Report Everything Else: A Pragmatic Proposal for Denying Mass Killers the Attention they Seek and Deterring Future Offenders,” American Behavioral Scientist 62, no. 2 (2018): 260–79.

60. Katharine Poppe, N. H.: A Case Study in Lone-Actor Terrorism (George Washington University, Program on Extremism, 2018).

61. D. R., Manifesto of the Charleston Church Shooter, Copy obtained by the authors, 2015; Hansi Lo Wang, “Alleged Shooter Visited Slave Plantations Before Church Shooting,” NPR, June 23, 2015, https://tinyurl.com/cz9jvtyf.

62. Poppe, N. H.: A Case Study in Lone-Actor Terrorism.

63. Daniel Politi, “D.R. has at Least One Black Friend who Denies Alleged Shooter is Racist,” Slate, June 2015, https://slate.com/news-and-politics/2015/06/dylann-roof-has-at-least-one-black-friend-who-denies-alleged-shooter-is-racist.html.

64. Erik Ortiz and Daniel Arkin, “D. R. ‘Almost Didn’t Go Through’ with Charleston Church Shooting,” NBC News, June 19, 2015, https://www.nbcnews.com/storyline/charleston-church-shooting/dylann-roof-almost-didnt-go-through-charleston-church-shooting-n378341.

65. See note 17 above.

66. Anderson, “The Bitter Life and Sudden Death of A.C.”

67. Adam Lankford and Jason R. Silva, “Sexually Frustrated Mass Shooters: A Study of Perpetrators, Profiles, Behaviors, and Victims,” Homicide Studies 28, no. 2 (2024): 196–219; Taylor, “O. M. May Not Have Understood the Difference Between ISIS, Al-Qaeda and Hezbollah.”

68. See note 66 above.

69. P. G., Manifesto of the Buffalo Supermarket Shooter, Copy obtained by the authors, 2022.

70. Borum, Psychology of Terrorism; Gartenstein-Ross et al., “Composite Violent Extremism”; Hafez and Mullins, “The Radicalization Puzzle”; Holbrook and Horgan, “Terrorism and Ideology”; Horgan, Terrorist Minds; Khalil, Horgan, and Zeuthen, “The Attitudes-Behaviors Corrective (ABC) Model of Violent Extremism”; Lankford, “The Myth of Martyrdom”; Neumann, “The Trouble with Radicalization”; Post, “Current Understanding of Terrorist Motivation and Psychology.”

71. Peter Langman, “Influences on the Ideology of E.H. (version 1.3),” School Shooters Info, 2016.

72. For example, the Global Terrorism Database has the Columbine incident coded as “yes” for their researchers doubting whether it meets the definition of terrorism at all.

73. Eric Bailey and Robin Fields, “Shootout Vowed in Chilling Video,” Los Angeles Times, September 11, 2001, https://www.latimes.com/archives/la-xpm-2001-sep-11-mn-44550-story.html.

74. Public Safety Commission, Marjory Stoneman Douglas High School Public Safety Commission Initial Report (Public Safety Commission, 2019).

75. Information obtained by one of the authors during the MBTAT Threat Assessment Symposium, “Complexities in Threat Assessment: An Advanced Look.”

76. Rick Braziel, Frank Straub, George Watson, and Rod Hoops, “Bringing Calm to Chaos: A Critical Incident Review of the San Bernardino Public Safety Response to the December 2, 2015, Terrorist Shooting Incident at the Inland Regional Center,” Office of Community Oriented Policing Services, 2016, https://portal.cops.usdoj.gov/resourcecenter/Home.aspx?page=detail&id=COPS-W0808.

77. Christal Hayes, “Waffle House Suspect T.R. Deemed Himself a ‘Sovereign Citizen,’ Part of Anti-Government Group,” USA Today, April 22, 2018, https://www.usatoday.com/story/news/2018/04/22/waffle-house-suspect-travis-reinking-sovereign-citizen/540543002/.

78. National Threat Assessment Center, Mass Attacks in Public Spaces: 2016–2020.

79. Marilyn Elias, “Sikh Temple Killer W.M.P. Radicalized in Army,” Southern Poverty Law Center, November 11, 2012, https://www.splcenter.org/fighting-hate/intelligence-report/2012/sikh-temple-killer-wade-michael-page-radicalized-army.

80. Ibid.

81. As noted earlier, survey results suggest 13 million U.S. adults “strongly approve” of Trump supporters taking over the Capitol building on January 6, 2021, and 7.8 million U.S. adults “strongly” believe it is acceptable to hold neo-Nazi or white supremacist views. However, there is a difference between voicing these opinions when surveyed and actively consuming extremist content. Furthermore, in a country with nearly 260 million adults, 13 million represents only five percent, and 7.8 million represents only three percent. Even if they were summed (based on the dubious assumption that they are non-overlapping groups), that would fall far short of the one-quarter of mass shooters we found with documented interests in extremism.

82. Lankford, Silver, and Cox, “An Epidemiological Analysis of Public Mass Shooters and Active Shooters.”

83. Public Safety Commission, Marjory Stoneman Douglas High School Public Safety Commission Initial Report.

84. Of course, role model influence is not the sole cause of copycat attackers’ behavior, and many other factors play a role. The vast majority of people do not commit mass shootings, no matter what they see in the news.

85. Langman, “Irrational Rationales”; Lankford, “The Myth of Martyrdom”; Post, “Current Understanding of Terrorist Motivation and Psychology”; Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats.”

86. Gartenstein-Ross and Blackman, “Fluidity of the Fringes”; Gartenstein-Ross et al., “Composite Violent Extremism”; Joint Counterterrorism Assessment Team, Mixing Ideologies Requires Multipronged Terrorism Prevention Efforts; Koehler, “Switching Sides”; Mattheis et al., “The Allen, Texas, Attack”; Meleagrou-Hitchens and Ayad, The Age of Incoherence?; Wray, “FBI Director Christopher Wray Testifies on January 6 Capitol Attack”; Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats.”

87. Caroline Logan, Randy Borum, and Paul Gill, Violent Extremism: A Handbook of Risk Assessment and Management (UCL Press, 2023).

88. Gartenstein-Ross and Blackman, “Fluidity of the Fringes”; Gartenstein-Ross et al., “Composite Violent Extremism”; Joint Counterterrorism Assessment Team, Mixing Ideologies Requires Multipronged Terrorism Prevention Efforts; Koehler, “Switching Sides”; Mattheis et al., “The Allen, Texas, Attack”; Meleagrou-Hitchens and Ayad, The Age of Incoherence?; Wray, “FBI Director Christopher Wray Testifies on January 6 Capitol Attack”; Wray, “Statement by Director Christopher Wray Before the U.S. House Select Intelligence Committee Hearing on Global Threats.”

89. Lankford, Silver, and Cox, “An Epidemiological Analysis of Public Mass Shooters and Active Shooters”; Peterson and Densley, “The Violence Project Database of Mass Shootings in the United States.”

90. See note 40 above.

91. Huff‐Corzine and Corzine, “The Devil’s in the Details”; Parkin and Gruenewald, “Open-Source Data and the Study of Homicide.”

92. Capellan et al., “Disaggregating Mass Public Shootings”; Lankford, “A Comparative Analysis of Suicide Terrorists and Rampage, Workplace, and School Shooters in the United States from 1990 to 2010”; Peterson and Densley, “The Violence Project Database of Mass Shootings in the United States.”

93. Joshua D. Freilich, Steven M. Chermak, Ralph Belli, Jeff Gruenewald, and William S. Parkin, “Introducing the United States Extremist Crime Database (ECDB),” Terrorism and Political Violence 26, no. 2 (2014): 372–84; Ashmini Kerodal, Joshua D. Freilich, and Steven M. Chermak, “Commitment to Extremist Ideology: Using Factor Analysis to Move Beyond Binary Measures of Extremism,” Studies in Conflict & Terrorism 39, nos. 7–8 (2016): 687–711; Gary LaFree and Laura Dugan, “Introducing the Global Terrorism Database,” Terrorism and Political Violence 19, no. 2 (2007): 181–204.

94. LaFree and Dugan, “Introducing the Global Terrorism Database.”

95. See note 26 above.

96. Alan Abramowitz and Jennifer McCoy, “United States: Racial Resentment, Negative Partisanship, and Polarization in Trump’s America,” The ANNALS of the American Academy of Political and Social Science 681, no. 1 (2019): 137–56.

97. See note 17 above.

98. Wray, “FBI Director Christopher Wray Testifies on January 6 Capitol Attack.”

Additional information

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Notes on contributors

Adam Lankford

Adam Lankford is a Professor and Chair of the Department of Criminology and Criminal Justice at The University of Alabama. He is the author of two books and many peer-reviewed studies on criminal behavior. His findings have been published in a variety of scientific journals and cited by The White House, by every major media outlet in the United States, and by international media from more than 40 countries.

Jason R. Silva

Jason R. Silva is an Assistant Professor in the Department of Sociology and Criminal Justice at William Paterson University. Silva’s research examines mass shootings, terrorism, school violence, and mass media. His recent publications have appeared in Justice Quarterly, Studies in Conflict & Terrorism, Homicide Studies, International Journal of Comparative and Applied Criminal Justice, and Journal of Policing, Intelligence, and Counter Terrorism.