What made Däter's case particularly difficult to detect was his professional access: dismissed twice for stealing from patients, he nonetheless retained the trust of elderly former clients who allowed him into their homes without suspicion. Five of his six victims were initially certified as having died of natural causes, and only his confession prompted investigators to look back at deaths across the Bremerhaven region. The murders were instrumental in nature, carried out to settle personal debts, and he told police he would have continued had he not been caught.

His career traced a path through the institutional core of the Nazi system — from early party membership to command of a concentration camp — making him part of the administrative apparatus that made mass atrocity possible. The roles he occupied were not incidental; they placed him at successive points of enforcement and control within a regime built on systematic violence.

Mackay's case illustrates the long institutional tail of violent offending — a formal diagnosis of psychopathy in adolescence, convictions for multiple killings in the 1970s, and decades of parole refusals that continue into the present. The true extent of his crimes remains contested, with fresh investigations as recently as 2020 failing to resolve longstanding suspicions about additional victims. His case remains active in the British parole system, drawing continued public and political attention more than fifty years after his offenses.

What distinguished List from many killers was not the act itself but the methodical calm that preceded and followed it — the meticulous planning, the letters left behind, and the nearly two decades he spent living quietly under an assumed name before America's Most Wanted brought his face back into public view. His stated motivations blended financial desperation with a particular strain of religious reasoning, making his case a subject of ongoing interest to criminologists and journalists alike.