The use of Zyklon B on the U.S.-Mexican border was a matter of keen interest to the firm of DEGESCH. In 1938, Dr. Gerhard Peters called for its use in German Desinfektionskammern. Romo has tracked down an article Peters wrote in a German pest science journal, Anzeiger für Schädlingskunde, which featured two photographs of El Paso delousing chambers. Peters went on to become the managing director of DEGESCH, which handled the supply of Zyklon B for the Nazi death camps. He was tried and convicted at Nuremberg. Hilberg reports that he got five years, then won a retrial that netted him six years. He was re-tried in 1955 and found not guilty.
Or that they designed their gas chambers after US Border Patrol's gas chambers and used the same chemical.
wait what?
https://www.counterpunch.org/2016/03/18/a-short-history-of-zyklon-b-on-the-us-mexican-border-please-dont-share-with-donald-trump/