Now a new book tells the story of Boix, a Spanish Republican prisoner sent to Mauthausen, who had fled Spain after the Nationalists of General Francisco Franco won the Spanish Civil War.
Once in France, he joined the French Foreign Legion and French Army and was captured in 1940 by the Germans, becoming one of the estimated 8,000 Spaniards to be taken to Mauthausen concentration camp, near the Austrian city of Linz.
He was imprisoned in the camp from January 1941 to May 1945.
Boix had worked as a news photographer and because of his skills was put to work in the SS photographic service, which stored over 60,000 photographs taken by Hitler's paramilitary force, many of which would be sent on to the Nazi High Command in Berlin.
He managed to smuggle out thousands of photographs which would go on to open people’s eyes to the horror behind the barbed wire fences and would subsequently provide key evidence during several high profile Nazi war trials.
At the Nuremburg trials, Boix was called as a witness by the French prosecution to show the SS photographs, which depicted the conditions in which prisoners had to live in the camp. During the trial, the prosecution had had some trouble proving that Ernst Kaltenbrunner had ever visited Mauthausen, but Boix’s testimony and most importantly, his photographs, proved that the Nazi leader had been at the camp.
Kaltenbrunner was one of the highest level leaders to be convicted during the trial and was executed after being found guilty of war crimes and crimes against humanity.
On May 5th 1945 soldiers from the 41st Reconnaissance Squadron of the US 11th Armoured Division of the US Army liberated Mauthausen concentration camp.
It is thought that around 8,000 Spanish Republicans were deported to Mauthausen during the Second World War, with around half dying in the camp.
"It was very bad in the camp for Spanish prisoners after 1943," historian Benito Bermejo, the author of a book entitled El fotógrafo del horror (The Photographer of Horror), told Spanish daily El Mundo.
"Only few survived, like Boix, who because of his skills as a photographer, received better treatment than his compatriots," Bermejo explained.
Boix escaped with his life, but his time in the concentration camp would have a lasting effect on his health. He died at the age of 30 from liver problems stemming from his time as a prisoner.