Following the defeat of Germany in World War II, he helped Nazis escape to Argentina, finally fleeing there himself.
Under the assumed name of Juan Maler, Kopps was hiding in the small town of Bariloche in the Andes Mountains.
In order to deflect attention away from himself, he told Donaldson that an even worse war criminal, Erich Priebke, was also living there, confirming ABC News' research.
Priebke was soon arrested, and Kopps temporarily fled to Tierra del Fuego.
The story was made for ABC's Primetime Live, as well as Nazi Hunters.