After Germany invaded Poland on September 1, 1939, Siegfried fled with a friend. They attempted to get papers allowing them to go to France, but were turned over to the Germans. Siegfried was jailed, taken to Berlin, and then transported to the Sachsenhausen camp near Berlin in October 1939. He was among the first Polish Jews imprisoned in Sachsenhausen. Inmates were mistreated and made to carry out forced labor. After two years, Siegfried was deported to the Gross-Rosen concentration camp, where he was forced to work in the stone quarry. In October 1942, Siegfried was deported from Gross-Rosen to the Auschwitz camp in occupied Poland. While there, Siegfried tried to use his experience as a pharmacist to save ill prisoners. As Soviet forces approached the Auschwitz camp in January 1945, Siegfried was forced on a death march from the camp. Those prisoners who could not continue or keep up were killed. Siegfried survived.
In the evening in Sachsenhausen we got a piece of bread, a quarter of one bread, and, uh, a piece of margarine or a, a piece of sausage, and this was exchanged again. The religious one they didn't want to eat the sausage, so we exchanged it with a piece of bread, or sometimes, uh, uh, we got, uh, what was it, yeah we exchanged it, so they can eat it. And later on, at night, for instance, we laid down, and we were happy we can rest, but they didn't let us rest at night either. They came through the windows and through the doors with water hoses, wetted us, jumped over us, stepped on us, one thing...this way they killed again. I don't know the reasons, sometimes we thought, oh, there is maybe a victory so they got drunk, and they came and did what they wanted with us.