After Franco defeated the Republican Army in Spain, Boix, like many others, fled over the Pyrenees into France. When World War II broke out, Boix joined the French Foreign Legion and was captured at Belfort in June 1940. As a former Spanish Republican, he was earmarked for a concentration camp, marked by a triangular patch with an “S” emblazoned on it. He was one of 8,000 Spanish refugees sent to the camps, of which around 2,000 survived.
On discovering that Boix was a photographer, the Nazis sent him to Mauthausen, which was known as Knochenmühle — the bone grinder. It was also where the SS’ official photographic identification service was located. They took photographs of all new prisoners at the camp, as well as ethnographic photographs to support Nazi racial theories. The two SS photographers who worked there also documented public executions and visits by high-ranking members of the Nazi party. Some of the more grotesque photos were simply taken as “souvenirs for SS members,” according to Lloyd.