Two years later, he completed his philosophy studies, earning an Master of Arts degree (later, he also earned a Doctor of Philosophy in philosophy, writing about works of Auguste Comte, under supervision of Professor Władysław Tatarkiewicz).
He also worked as a publicist, using the pseudonym Andrzej Witkowski. Mosdorf died in Auschwitz concentration camp in 1943, killed for helping Jews. Mosdorf associated himself with the National Democratic movement (founded by Roman Dmowski) some time in 1926.
He wrote articles for nationalist magazines, always claiming that Germany was Poland’s main enemy and that Poland should gain control over the Western part of Upper Silesia and Masuria.
In 1928, during the IV Congress of the MW, which took place in Lwów, he was elected director of the organization. We are not fascists, nor Hitlerites, for we are a native Polish movement, independent of foreign views.
Additionally, we do not see ourselves as fascists or Nazis due to the many weaknesses, and even sins, these movements carry. These are not examples we would want to follow.- January Mosdorf "Wczoraj i Jutro", 1938
In late 1939, after Polish September Campaign, he returned to the conspirational National Party.
He was one of leaders of the party, and he helped with the creation of the anti-Nazi paramilitary units known as Narodowa Organizacja Wojskowa.
In July 1940, Mosdorf was arrested and placed in Gestapo"s infamous Pawiak prison. On January 6, 1941, he was sent to Auschwitz. While there, Mosdorf met his friend from Office of Naval Research, Bolesław Świderski, whose support was crucial.
Until then, Mosdorf had regarded Jews as enemies of Poland and the Polish nation.
After surviving typhus, however, he changed his attitude and started to help fellow inmates, regardless of their nationality and religion. In Auschwitz, where he knew that Jews were being exterminated, he organized a group that helped those in need.
He was a very active member, procuring food and clothes for starving and cold inmates. Professor Irina Livezeanu from University of Pittsburgh wrote: "Mosdorf did everything in his power to help the Jews in the Auschwitz camp, and he died together with the Jews."
Details of Mosdorf"s death are unknown.
Reportedly, he was denounced either by a Belarusian anti-semite or by Józef Cyrankiewicz, who later became prime minister of communist Poland.
On September 25, 1943, Mosdorf was placed in the Pavilion XI, and on October 11 he was executed with a group of other inmates. His symbolic tomb is located at the Powązkowski Cemetery in Warsaw.
As a student, he was a member of several right-wing youth organizations. Mosdorf was widely liked by fellow members of the MW. His appearances were always associated with applause.
Later on, he had to hide for some time because he was a member of the Office of Naval Research, and the government had incarcerated several activists of the organization in the Bereza Kartuska prison.
