Leakage is one of the eight warning behaviors referred to in the violence risk and threat assessment literature. Previous research has highlighted the relevance and prevalence of leakage in lone-actor terrorists; however, a more detailed understanding of this phenomenon is lacking. This study sets out to expand our knowledge of this behavior by conducting an exploratory analysis using court records relating to IS-inspired lone-actor terrorism cases in the United States. The general patterns in leakage warning behavior were analyzed, and different types of leakage were examined with regard to from whom they were leaked, how they were leaked, their presence online, and whether or not they occurred before certain types of attacks more than others. It was found that leakage in the form of support tended to be leaked most frequently to members of the public, via written text and online, whilst the leakage of intent and specifics appeared to be more regularly leaked to co-conspirators and through verbal communication that avoided the online world. Significant relationships were also found between leakage, FBI interaction and attack initiation, but no significant relationship was found between leakage and mental health. The implications of these findings are discussed.
