– Executive Summary

Anticipating, preventing, and mitigating acts of terrorism and targeted violence remains an ongoing and urgent challenge for law enforcement and homeland security practitioners. Despite several high-profile cases in recent years where a triggering event—referred to herein as a catalytic event—appeared to directly impact a perpetrator’s mobilization to violence, traditional law enforcement prevention and mitigation frameworks have not formally integrated the concept of catalytic events. This thesis defines a catalytic event as an external occurrence that plays a significant role in mobilizing a malicious actor to plan or carry out an act of violence. These are events to which the perpetrator may not have a direct, personal connection but that contribute meaningfully to a violent outcome; examples include political developments, controversial court rulings, police-involved shootings or uses of force, civil unrest or protests, global crises such as the COVID-19 pandemic, or other high-profile attacks.

Through an analysis of 11 plots and acts of violence triggered, at least in part, by three catalytic events—the COVID-19 pandemic, the police murder of George Floyd, or the 2020 presidential election—this thesis seeks to gain insight into the ways in which catalytic events mobilize individuals to violence. Two primary research questions guide this analysis: 1) What role do catalytic events play in mobilizing individuals to violence? and 2) How should law enforcement agencies position themselves to anticipate, prevent, and mitigate violence linked to a catalytic event? This thesis uses a structured, focused comparison—a method which involves asking general questions of each case to standardize data collection and focus on aspects most relevant to the research objective.[1]

In examining how catalytic events interact with other risk factors, this thesis finds that catalytic events have the potential to trigger a broad range of individuals to violence. Perpetrators of plots and acts of violence in this analysis have ties to a variety of extremist ideologies, beliefs, and/or mindsets, including racially and ethnically motivated violent extremism, extremist conspiracies, and anti-government, anti-authority violent extremism. They also vary in terms of their struggle with personal stressors and mental health issues, as well as their criminal history. Another key finding is that catalytic events play a significant role in altering or determining a perpetrator’s target selection and the timing of their attack. This thesis finds that individuals triggered by a catalytic event often rapidly mobilize to violence—in some cases, within days—highlighting the need for early detection and swift action to prevent and mitigate violent outcomes.

Based on findings from the case studies, this thesis presents an initial typology—or way of conceptualizing—different “types” of catalytic event-driven violence and implications for law enforcement. It proposes that catalytic events trigger an individual to violence in three primary ways:

  1. Presenting a perceived opportunity to maximize violence or capitalize on chaos. The catalytic event directly guides the target selection and timing of these perpetrators, who may have already been on law enforcement’s radar and considering or planning for violence. Given the opportunistic nature of these perpetrators, they may seek to attack high-value targets in terms of casualty numbers and publicity.
  2. Exacerbating grievances and contributing to radicalization. The catalytic event appears to be the primary determinant of violence for these perpetrators, potentially triggering those with no prior links to extremist ideologies or plans for violence. These individuals may prioritize symbolic targets, including groups that lie at the center of their rage or public officials they perceive as responsible for policies linked to their grievances.
  3. Compounding personal stressors, resulting in violence that may appear impulsive and/or random. For these perpetrators, the catalytic event interacts with personal triggers in a way that causes them to engage in spontaneous violence. Targets may be seemingly random, including locations that the perpetrator happens to frequent.

Since it remains difficult to predict which “type” of catalytic event-driven violence is most likely to emerge, an optimal approach to prevention and mitigation would involve identifying likely targets of each “type” within an agency’s area of responsibility, allowing for more effective prioritization and allocation of resources to confront threats. Table 1 outlines potential countermeasures and their applicability to each “type.”

 “Type” of Catalytic-Event Driven Violence
Law Enforcement Prevention & Mitigation MeasuresOpportunisticGrievance-BasedPersonal Stressors
Assess resonance of catalytic event with current subjects of concernXX
Implement or enhance protective measures at certain locations or for specific individualsXX
Enhance situational awareness and preparedness of relevant stakeholdersXX
Emphasize partnerships with entities likely to frequently interact with individuals of concernX
Track online threats and violent extremist propaganda linked to catalytic eventXXX
Table 1: Countermeasures by “Type” of Catalytic Event-Driven Violence

This thesis confirms the significant role of catalytic events in sparking acts of violence and aims to provide law enforcement with an initial set of tools for incorporating them into violence prevention and mitigation frameworks. The complexity of the subject necessitates further research and continuous refinement of the typology, with the goal of eventually leveraging it to develop or formalize relevant policies and procedures within a law enforcement agency and evaluating the success of its application. Recent targeted acts of violence and a flood of online threats in reaction to specific events—such as the Supreme Court’s overturning of Roe v. Wade and criminal indictments brought against former President Donald Trump—reiterate the significance of this research, while forthcoming developments—including the 2024 presidential election—signal a sense of urgency.


[1] Alexander L. George and Andrew Bennet, “Chapter 3: The Method of Structured, Focused Comparison,” in Case Studies and Theory Development in the Social Sciences (Cambridge, MA: MIT Press, 2005), 67–72.

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