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June 4, 2026

AUTHORS
Jaclyn Schildkraut
Hunter Martaindale
Emily Greene-Colozzi

Executive Summary

This report examines 171 mass public shootings in the United States between 1999 and 2024 involving 175 perpetrators with identifiable pre-attack warning behaviors and communications. Using the Path to Intended Violence framework, the findings highlight consistent patterns in perpetrators’ experiences, behaviors, and communications prior to the attacks. The findings are intended to support efforts to identify, interpret, and respond to warning signs prior to acts of targeted violence.

Key findings from the report include:

• Mass public shootings occur across a wide range of locations and contexts.
  Incidents were most common in workplaces (25.1%) and schools (24.6%), though they occurred across 39 states and the District of Columbia and at all times of day and week.
  These patterns reinforce the need for prevention efforts that extend across multiple settings and communities.
• Perpetrators often experience multiple, overlapping stressors.
  Mental health concerns (64.6%), job-related difficulties (51.4%), and family-related problems (50.3%) were among the most common. On average, perpetrators experienced about five different stressors, indicating that challenges rarely occurred in isolation.
  This underscores the importance of recognizing cumulative stressors rather than focusing on any single issue.
• Many perpetrators have prior contact with law enforcement.
  Nearly two-thirds (64.0%) had prior interactions with law enforcement, including for both violent and nonviolent behaviors.
  These prior contacts may represent opportunities for earlier intervention.
• Firearms are most commonly obtained through legal channels.
  Among cases where acquisition could be determined, the most common source was purchase from a federal firearms licensee (59.6%), followed by access within the home.
  This highlights the importance of considering multiple points of access in prevention strategies.
• Planning behaviors vary widely in duration and scope.
  When identifiable, planning ranged from same-day attacks to preparation over several years. On average, perpetrators spent approximately 10 months planning their attacks.
  This variability suggests that opportunities for intervention may exist across different timelines.
• Leakage is common and often communicated to others.
  A majority of perpetrators (85.7%) engaged in leakage, or the communication of violent thoughts or intentions, prior to the attack, most often through direct, in-person interactions.
  This finding highlights the critical role of bystanders in recognizing and responding to warning signs.
• Leakage is frequently observed by individuals within perpetrators’ social networks.
  Friends, family members, and coworkers were among the most common observers, and in many cases, leakage was known across more than one type of observer.
  These patterns suggest that relevant information may be distributed across multiple individuals.
• Leakage content frequently centers on violence and harm.
  More than half of perpetrators referenced violence or death (55.4%), with many also discussing killing others (48.6%), suicide or self-harm (41.1%), or mass shooting-specific violence (40.0%).
  These themes may serve as important indicators of escalating risk.
• Threats are commonly embedded within leakage.
  Nearly two-thirds of perpetrators (64.6%) made at least one type of threat, most often direct threats.
  Understanding different forms of threats can support more effective identification and response.
• Perpetrators often exhibit multiple concerning behaviors.
  Indicators such as emotional distress, impulsivity, risky behavior, and social withdrawal frequently co-occurred, with individuals demonstrating an average of more than six concerning behaviors.
  These findings emphasize the importance of recognizing patterns of behavior rather than isolated actions.

Across these findings, a consistent pattern emerges: warning signs often are present, observable, and distributed across multiple individuals and systems prior to an attack. These results highlight the importance of recognizing patterns of behavior and communication over time, as well as the critical role of information sharing in preventing acts of mass violence. They also underscore the value of training efforts that support bystanders and community members in identifying and responding to concerning behaviors and communications.

View the full report.

Visit the project webpage.