Studies concerning both mental disorder and involvement in terrorism have a long and convoluted history. The literature that has focused on attempting to understand psychological drivers of terrorist behaviour has shifted through multiple stages. Moving from untested assumptions of psychopathology, personality, and deviance, towards more empirically sound interpretations of sociology. While the early studies were correctly debunked on methodological grounds, the existing consensus, spawned from the growing interest in sociology, that mental disorder never plays a role in terrorism, is likely to be a fallacy when we consider the complexity of the problem and the diverse pool of individuals who engage in it. This piece of research falls into line with highly influential seminal reviews, and more recent re-examinations of the role of group processes in terrorism. Taking the starting position that the logic of an act of targeted violence being either borne out of mental health problems or terrorism is likely to be a false dichotomy. Instead, we are likely to see a range of mental disorders across the arc of terrorist involvement. Using multiple existing and novel inferential statistical techniques on both qualitative and quantitative datasets, this work addresses the current discord both in the understanding of the potential role of psychopathology, and to re-examine currently well accepted, but as yet untested theories of terrorist behaviour. The intent of this multi-pronged methodology is to provide practitioners with a holistic understanding of the problem as well as suggestions toward preventing and disrupting future offences.