The purpose of this study is to understand the behavior of lone actor terrorists and solo mass murderer attackers. Rather than use the terms 'terrorist' or 'offender' as dependent variables, the researchers disaggregate and compare socio-demographic, psychological and behavioral features between these two offender types.
The study relied on open source methodology, using sources already available in the public domain for raw data. Initial actor dictionaries for lone actors and mass murderers were compiled from academic literature on the respective topic area. Further names of lone actors were added through LexisNexis searches for English-language news, the Global Terrorism Database, and lists of convictions of terrorism-related offenses. Further names of mass murderers were added through database searches (Mother Jones, USA Today, Mayors Against Illegal Guns), LexisNexis searches, and FBI Uniform Crime Reports. Other resources included public record depositories and biographies of specific lone actors. Following data coding, the researchers used bivariate and multivariate tests to analyze the data.
All United States-based individuals who a) fit the study definition of lone actor terrorist or solo mass murderers (please refer to the User Guide for more details), b) were identifiable through publicly available records and sources, and c) operated between 1990 and 2013. The final sample contains 71 lone actors and 115 mass murderers (n = 186).
Longitudinal: Cohort / Event-based
All identifiable individuals in the United States who fit the study definition of lone actor terrorist or solo mass murderer from 1990 to 2013, and who were identifiable through publicly available sources.
Variables are broadly grouped based on factors prior to, during, and following the attack for each individual. Sociodemographic variables are also included.
- Sociodemographic items: Gender, year of birth, relationship status, occupation, parental status, education, military experience, citizenship, religion, ideology, age/year of first terrorist activity, any arrests and/or criminal convictions
- Pre-event items: Grievances and other contributing factors to individual's social and psychological state (e.g. having been harmed, humiliated, or wronged; history of substance abuse or mental illness; recent or chronic stress; family, relationship, or financial issues; social isolation; changes in ideology; changes in work/school performance), whether a tipping point occurred, leakage-related behaviors (e.g. verbalizing intent and desire to hurt others, if others were involved or aware of planning)
- Event items: Nature of target and location, type of event, attack method(s), number of people injured or killed in the attack
- Network-related activities: Attempts to recruit others, interacted with or joined a wider network offline or online, wrote public statements, if family or associates were also involved, read material about other offenders
- Post-event items: If individual was killed in the event, claimed responsibility, felt remorse, possessed materials publicizing their actions