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Improving the Understanding of Mass Shooting Plots

NCJ Number
John S. Hollywood
Date Published
June 2022
35 pages

The authors used data on mass shooting plots to create an online Mass Attacks Defense Toolkit, by analyzing threat indicators, their identification and investigative procedures, identifying potential active shooters while reducing the burden on police agencies, recognizing and mitigating barriers to discovering and halting active shooter plots, and identifying key factors that impact the potential casualties.


This project expanded on the earlier U.S. Terrorist Incidents and Plots (TIPS) database to include attempted and completed mass shooting plots. As a result of their work, the researchers developed an online Mass Attacks Defense Toolkit for use by law enforcement officers and government agencies involved in prevention and response, policymakers, funders, and the public. The research team collected data on mass shooting plots, including plots foiled in advance or on-scene of the attack, from both open and previously un-released sources, official records from law enforcement  agencies to identify possible indicators of mass shooting plots, models for prioritizing investigations, process and policy barriers to foiling plots along with solutions, and factors contributing to plot lethality along with ways to defend against them. The authors employed analytical methods used in terrorism research to identify false positive cases for use as a control group; for plot lethality characteristics, the authors collected data on perpetrator, bystander, and first responder behaviors in order to identify ways to strengthen security in public soft target locations. Authors’ recommendations include institutional support for interagency teams; public education on how to report suspected mass shooting plots; public education on what suspicious seekers look like in their efforts to acquire guns and tactical gear; the need for wellness checks for people who are a potential danger to themselves or others; the importance of risk assessment tools which are identified in the Toolkit; the need for sponsorship of coordinated response planning and training among law enforcement; and coordinated post-attack actions to help survivors and first responders.