This article analyzes the sociodemographic network characteristics and antecedent behaviors of 119 lone-actor terrorists. This marks a departure from existing analyses by largely focusing upon behavioral aspects of each offender. This article also examines whether lone-actor terrorists differ based on their ideologies or network connectivity. The analysis leads to seven conclusions. There was no uniform profile identified. In the time leading up to most lone-actor terrorist events, other people generally knew about the offender’s grievance, extremist ideology, views, and/or intent to engage in violence. A wide range of activities and experiences preceded lone actors’ plots or events. Many but not all lone-actor terrorists were socially isolated. Lone-actor terrorists regularly engaged in a detectable and observable range of activities with a wider pressure group, social movement, or terrorist organization. Lone-actor terrorist events were rarely sudden and impulsive. There were distinguishable behavioral differences between subgroups. The implications for policy conclude this article.

An open source sample of 111 lone-actor terrorists from the United States and Europe were studied through the lens of the Terrorist Radicalization Assessment Protocol (TRAP-18). This investigative template consists of 8 proximal warning behaviors and 10 distal characteristics for active risk management or active monitoring, respectively, by national security threat assessors. Several aspects of criterion validity were tested in this known outcome sample. Seventy percent of the terrorists were positive for at least half or more of the indicators. When the sample was divided into Islamic extremists, right-wing extremists, and single-issue terrorists, there were no significant differences across all 18 indicators except for 4. When the sample was divided according to successful versus thwarted attackers, the successful attackers were significantly more fixated, creative, and innovative, and failed to have a prior sexually intimate pair bond. They were significantly less likely to have displayed pathway warning behavior and be dependent on a virtual community of likeminded true believers. Effect sizes were small to medium (ϭ 0.190-0.317). The TRAP-18 appears to have promise as an eventual structured professional judgment risk assessment instrument according to some of the individual terrorist content domains outlined by Monahan (2012, 2016).

We test whether significant differences in mental illness exist in a matched sample of lone-and group-based terrorists. We then test whether there are distinct behavioral differences between lone-actor terrorists with and without mental illness. We then stratify our sample across a range of diagnoses and again test whether significant differences exist. We conduct a series of bivariate, multivariate, and multinomial statistical tests using a unique dataset of 119 lone-actor terrorists and a matched sample of group-based terrorists. The odds of a lone-actor terrorist having a mental illness is 13.49 times higher than the odds of a group actor having a mental illness. Lone actors who were mentally ill were 18.07 times more likely to have a spouse or partner who was involved in a wider movement than those without a history of mental illness. Those with a mental illness were more likely to have a proximate upcoming life change, more likely to have been a recent victim of prejudice, and experienced proximate and chronic stress. The results identify behaviors and traits that security agencies can utilize to monitor and prevent lone-actor terrorism events. The correlated behaviors provide an image of how risk can crystalize within the individual offender and that our understanding of lone-actor terrorism should be multivariate in nature.

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ABSTRACT:This article provides an in-depth assessment of lone actor terrorists' attack planning and preparation. A codebook of 198 variables related to different aspects of pre-attack behavior is applied to a sample of 55 lone actor terrorists. Data were drawn from open-source materials and complemented where possible with primary sources. Most lone actors are not highly lethal or surreptitious attackers. They are generally poor at maintaining operational security, leak their motivations and capabilities in numerous ways, and generally do so months and even years before an attack. Moreover, the "loneness" thought to define this type of terrorism is generally absent; most lone actors uphold social ties that are crucial to their adoption and maintenance of the motivation and capability to commit terrorist violence. The results offer concrete input for those working to detect and prevent this form of terrorism and argue for a re-evaluation of the "lone actor" concept.

For the past forty years, researchers studied the relationship between mental disorder and terrorist involvement. The literature developed in four paradigms, each of which differs in terms of their empirical evidence, the specific mental disorders studied, and their conceptualizations of terrorist involvement. These paradigms have not, however, witnessed linear and incremental improvements upon one another. Although one paradigm has generally tended to dominate a temporal period, many false assumptions and incorrect interpretations of earlier work permeate into today's discourse. This paper provides a history of the study of mental disorders and the terrorist. First, we briefly outline the core fundamental principles of the first two paradigms, The paper then outlines the core arguments produced by the seminal reviews conducted in paradigm three. We highlight how these findings were consistently misinterpreted in subsequent citations. We then highlight recent innovations in the study of terrorism and mental disorder since the various influential literature reviews of 1997-2005. We conclude by outlining how future research in this area may improve in the coming years by broadening our understanding of both terrorist involvement and psychopathology away from simple dichotomous thinking.

This paper outlines the sociodemographic, developmental, antecedent attack, attack preparation, and commission properties of 115 mass murderers between 1990 and 2014. The results indicate that mass murderer attacks are usually the culmination of a complex mix of personal, political, and social drivers that crystalize at the same time to drive the individual down the path of violent action. We specifically focus upon areas related to prior criminal engagement, leakage, and attack location familiarity. Whether the violence comes to fruition is usually a combination of the availability and vulnerability of suitable targets that suit the heady mix of personal and political grievances and the individual's capability to engage in an attack from both a psychological and technical capability standpoint. Many individual cases share a mixture of unfortunate personal life circumstances coupled with an intensification of beliefs/grievances that later developed into the idea to engage in violence.