This is because Chaim Hirszman, the only other survivor of Bełżec,[4] joined the new communist militia in Stalinist Poland shortly after the war and was himself murdered in March 1946 by anti-communist forces before he was able to give a full account of his camp experience.

Reder, age 61, was deported to Bełżec on August 11, 1942,[6] with one of the first transports of Jews from the Lwów Ghetto after the new larger gas chambers were erected of brick and mortar.

A Ukrainian woman, his former employee, helped him first, as did the Polish Righteous Joanna Borkowska whom Rudolf Reder married after the war and later emigrated with, settling in Toronto, Canada.

Soon after the Soviet takeover, whilst still in Poland, Reder testified in January 1946 in Kraków before the Central Commission for Investigation of German Crimes (known as the Institute of National Remembrance at present).

His monograph titled Bełżec was written in Polish with the Preface by his editor, Nella Rost, and illustrated with a map by Józef Bau, a Holocaust survivor who studied at the Academy of Fine Arts.

[9] In the book, Reder wrote about what he saw as the motor-maintenance worker, and what he learned afterwards: A dozen or so SS men drove the women along with whips and fixed bayonets all the way to the building and from there up three steps to a hall.

[10] In 1960, he submitted a deposition at the prosecutor’s office in Munich as part of the German preparations for the Belzec trial against eight former SS members of Bełżec extermination camp personnel.

[12] His account of the Belzec camp imprisonment, published in 1946,[13] was reprinted in 1999 by Auschwitz-Birkenau State Museum with Fundacja Judaica in bilingual edition featuring an English translation by Margaret M. Rubel,[9] then issued again as "Belzec" in Polin: Studies in Polish Jewry (volume 13, 2000), and republished in the UK as part of a book titled I Survived a Secret Nazi Extermination Camp by Mark Forstater in 2013.