The recent attack at an Orlando night club has provoked both intrigue and confusion. Given the lack of an obvious operational connection to the Islamic State and the shooter’s rather rudimentary religious knowledge and history of mental instability, some voices have rightfully questioned the appropriateness of the label ‘terrorism’ to something that rather resembles mass school shootings. Journalist Ryan Cooper, for example, writes that the shooting was not organized terrorism but mass murder, and the “result of a single unbalanced person”. The attack underscores the point emphasized by researchers that radicalization to violent extremism is a complex, psycho-social process that belies a simple explanation and that the role played by mental illness in the radicalization process is not well understood. While not a “cause” of radicalization, research suggests that mental illness may contribute to violent extremism when it combines with a host of other factors, like emotional trauma, substance abuse, and extremist narratives.
An analysis of START’s Profiles of Individual Radicalization in the United States (PIRUS) dataset, which allows researchers to compare violent outcomes against non-violent criminal outcomes, suggests that those with evidence of mental illness are more likely to act out violently than those without such a history. More so, this study and others found that lone actors like Mateen are more likely to exhibit signs of mental illness than extremists who act as part of a group. And while the overall occurrence of mental illness in the dataset is low (ranging from 3.8% to 8.4%, depending on one’s assessment of the validity of sources), the relationship between mental illness and violent behavior is strong and positive across time and ideological preference.
The apparent relationship between mental illness and extremist violence stands against a lengthy and well-evidenced tradition of terrorism studies showing that most terrorists are psychologically normal. This makes quite a bit of sense; terrorist group leaders tend to emphasize the importance of ideological and religious knowledge, and most of all, the ability to acquire specialized skills, be they combat, logistical, propaganda skills, or other types thereof. Thus, groups like al-Qaeda core have typically not been interested in recruiting mentally unstable individuals, who are generally neither reliable nor controllable. This style of organizational preference seems to have fundamentally changed with the so-called Islamic State, for whom anyone will do; any operative and any type of attack. Unlike groups past, the Islamic State does not seem to care either way if its adherents are mentally healthy or not. Through a savvy social media campaign, they have doubled down on al-Qaeda in the Arabian Peninsula’s ‘Inspire’ magazine ethos, cultivating an organizational brand that emphasizes a ‘do-it-yourself’ approach.
However, most traditional research on terrorist decision-making focuses on groups, not individuals. At the individual level, radicalization is complex and over-determined; that is, there are multiple sufficient explanations for why radicalization occurs for any given case. In the case of Mateen, mental illness was one of many plausible factors that may have facilitated his radicalization. Some reports suggest that Mateen dealt with profound failure and rejection in his professional life following his swift termination as a prison guard and then as a private security guard. His past was marked by repeated violent behavior requiring psychological attention; he was convicted in juvenile court of battery, and repeatedly suspended for rule violations. It is possible that he may have dealt with issues of identity, torn between his Afghan and American roots in a complicated post-9/11 world.
Further obscuring the problem is that the link between mental health and radicalization is not limited to clinically diagnosable disorders alone. In some cases, an individual’s radicalization process can be better understood through a lens of traumatic emotional and personal experiences. Qualitative analysis of the same START study found that for some individuals, intense feelings of injustice, outrage, revenge or even love can potentially act as mechanisms to push people toward extremist violence. For example, Colleen LaRose, a.k.a. “Jihad Jane”, who was implicated in a plot to assassinate Swedish cartoonist Lars Vilks, suffered various types of physical and mental abuse in her youth, including repeated rape by her own father. Naser Jason Abdo, who conspired to attack an Army base in Fort Hood, TX, suffered humiliating harassment in the Army and grew up in a broken and abusive family environment, with both parents in and out of his life due to their criminal records. One of the Boston Marathon bombers, Tamerlan Tsarnaev, had a history of conflict-related traumas, domestic abuse, as well as untreated mental problems. Instances of such humiliation and personal failure, when combined with an extremist narrative offering personal redemption and self-worth, can interact in ways that are difficult, if not impossible to predict ahead of time, and can produce potentially dangerous outcomes.
Mental illness is certainly atypical in the broader population of terrorists. Yet given START’s recent research indicating that mental health conditions may be linked to higher propensities for violent behavior among extremists, it is crucial that we do more to understand the processes involved when these phenomena coincide. Future research efforts should focus on that question, while also considering other potentially compounding factors such as substance abuse and criminal history. Doing so will require a qualitative approach that focuses on causal mechanisms that unfold over time, as opposed to simple behavioral indicators. Radicalization researchers should draw on methods that account for causal complexity, such as process tracing, path dependency, and explanatory typologies, which are commonly used in related fields but have yet to be fully harnessed for understanding violent extremism.
The relationship between mental illness and radicalization is not simple, but is potentially very important. Indeed, it is a good sign that there is a growing consensus among researchers and practitioners that countering violent extremism efforts need to integrate mental health and social service professionals into prevention and intervention efforts. These experts have an important role to play in working with community leaders through awareness training to recognize at-risk individuals, building trust between communities and law enforcement, and implementing a more holistic approach to countering violent extremism. However, the integration of mental health and social service professionals in CVE programs is likely to fail unless we better understand the role that mental illness plays amongst a host of other factors that drive individuals toward extremism. This in turn can only happen once we move past simple indicators and embrace research methods that are designed to solve complex problems.
 According to an analysis of the PIRUS (Profiles of Individual Radicalization in the United States) dataset, only 8.4% of individuals (122 out of 1451) had some evidence of mental illness, either through a clinical diagnosis or popular speculation according to open sources. Among the 209 individuals in PIRUS without a known group affiliation, 25.8% of individuals had evidence of mental illness (54/209). This project was supported by Award Number 2012-ZA-BX-0005, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this op-ed are those of the authors and do not necessarily reflect those of the Department of Justice.
 Discussions are still ongoing whether or not these numbers merely reflect a regular proportion of the general population – a difficult question to accurately answer for social scientists reliant on open source information.