Using academic networks established before the war, Martin agreed to undertake a spying mission in Nazi Germany on behalf of the Front de l'Indépendance group to find reliable information on the fate of Belgian Jews deported to Eastern Europe.
Martin reported his findings about the mass extermination of Jews and was one of the first to provide detailed information on the functioning of the Auschwitz concentration camp.
At the request of the officials of the Comité de Défense des Juifs, he went to observe directly where the trains went that carried Belgium's deported Jews.
He obtained meetings with sociologist Leopold von Wiese at Cologne, and with another colleague at the University of Breslau (now Wrocław in Poland).
At Katowice, not far from Auschwitz, Martin met workers from the Service du Travail Obligatoire in a bistro, who described to him the mass extermination of Jews and the incineration of their bodies.
[3] After secretly returning to Belgium, he wrote a report (archived by the Yad Vashem Holocaust memorial) to his resistance comrades in the Front de l'Indépendance.