Researchers whose work centers on a specific form of serious violence, political terrorism and extremism, street gangs, or mass and serial homicide, studying the causes, patterns and prevention of that violence as a subject in its own right rather than through one general theory of crime. This group gathers the founders of major terrorism research databases and centers, researchers studying radicalization, extremism and political violence, researchers whose long fieldwork and ethnography documented how street gangs form and function, and researchers who built the empirical study of mass and serial murder. It excludes gang and subcultural researchers whose primary theoretical claim is about blocked opportunity producing a delinquent subculture, who belong under Strain, Anomie and Subcultural Theory, and excludes general policing policy researchers whose subject is not one specific violent crime type, who belong under Policing, Corrections and Justice System Research.