A Mixed Method Examination of Law Enforcement Investigatory Strategies Used in Jihadi and Far-right Foiled Terrorist Plots Before and After 9/11

Empirical research on the law enforcement strategies used to prevent terrorism has increased since the September 11, 2001 terrorist attacks. Yet, few studies have examined how these preventative approaches vary based on terrorists’ ideological affiliations and across time. This study thus explores the similarities and differences in law enforcement investigatory strategies used to thwart global jihadi and far-right terrorist violence prior to and since the 9/11 terrorism events. Employing a convergent parallel mixed method research design, our study analyzes both quantitative and qualitative data on 86 terrorism enterprise investigations from the U.S. Extremist Crime Database (ECDB). The quantitative data analyses examine patterns relating to how investigations are initiated, the agencies involved, and the roles of human intelligence in foiling terrorist violence. Complementary qualitative case narratives are then used to explore in more detail the investigatory process for a subset of cases. We discuss several noteworthy findings that have implications for both law enforcement practitioners as well as future scholarly research.