Kohlhepp operated for over a decade across Spartanburg County before his crimes were fully uncovered, his concealment aided in part by a successful career as a licensed real estate agent. His confirmed killings span thirteen years, beginning with a quadruple homicide at a motorcycle shop in 2003, and his eventual arrest in 2016 came only after a surviving victim was discovered chained inside a storage container on his rural property. The gap between his first known offense and his capture reflects both the deliberateness of his methods and the difficulty investigators faced in connecting crimes separated by years.

Operating for nearly two decades in Siberia and the Russian Far East, Popkov carried out one of the largest known serial killing campaigns in recorded history, with confirmed victims numbering in the dozens before investigations eventually produced a full accounting. His position as a law enforcement officer afforded him both opportunity and a degree of protection from suspicion, enabling the crimes to continue across multiple cities and an extended timespan.

Among the senior figures of the Nazi apparatus, Heydrich occupied a uniquely operational role — not merely an ideologue but an architect who built and ran the institutional machinery through which persecution became genocide. He oversaw the Gestapo, the SD, and the Kripo simultaneously, and it was he who chaired the Wannsee Conference, where the systematic deportation and murder of Europe's Jews was formally coordinated across state agencies. His effectiveness lay in combining intelligence work, bureaucratic control, and organized violence into a single administrative structure, making him central to translating Nazi policy into mass killing at scale.