As the longest-serving commandant of Auschwitz, he oversaw the industrialization of mass killing on a scale without precedent, refining procedures and infrastructure that processed victims by the hundreds of thousands. His role was not merely administrative — he actively sought more efficient methods, including the adoption of Zyklon B in the camp's gas chambers. The memoirs he wrote during his imprisonment before execution remain a primary document of how the machinery of genocide was built and maintained from within.

Cottingham operated for roughly fifteen years before his arrest, and the span of his confirmed crimes across two states suggests an ability to avoid detection that outlasted most investigations of the era. The mutilation of some victims — and the removal of identifying features — reflected deliberate effort to obstruct identification, a pattern that complicated law enforcement efforts for years. His later claims of up to eighty unconfirmed killings, made under non-prosecution agreements, have never been fully resolved, leaving the true scope of his activity uncertain.

Of the roughly 45,000 Union prisoners held at Camp Sumter during its fourteen months of operation, nearly 13,000 died from disease, malnutrition, exposure, and violence — a mortality rate that made Andersonville the deadliest site of the Civil War by some measures. Wirz oversaw the camp's daily administration during that period, and the conditions that developed under his command became the basis for the first war crimes trial in American history. He remains the only Civil War officer executed for war crimes.

His rise through Chile's military establishment was unremarkable until September 1973, when he led the coup that ended South America's longest-running democracy and inaugurated nearly two decades of authoritarian rule. Under his regime, thousands were killed, tortured, or forcibly disappeared through a systematic apparatus of state repression. The involvement of American intelligence services in facilitating the overthrow of a democratically elected government gave his seizure of power a Cold War dimension that extended well beyond Chile's borders.