Invented in Germany, Zyklon B was designed as an effective pesticide and rodenticide. When the sealed canisters were opened and the pellets exposed to air, the hydrogen cyanide would vaporize into a lethal gas. The manufacturer, Degesch (Deutsche Gesellschaft für Schädlingsbekämpfung), supplied it widely for pest control before and during World War II.

Beginning in 1941, Nazi officials modified the chemical—removing the standard warning odorant—and began using it for mass murder. It became the primary method of execution in the gas chambers at extermination camps like Auschwitz-Birkenau and Majdanek. The pellets were dropped into the packed chambers, where the vapor caused rapid unconsciousness and death through internal asphyxiation.

The scale of its use is well-documented; records show that at least 25 tons of Zyklon B were delivered to Auschwitz alone between 1942 and 1944. Surviving invoices, supply orders, and postwar testimonies provide irrefutable historical evidence of its application in the extermination of approximately 1.1 million people.