After his parents and other family members were killed in the ghetto in 1941, Joseph and his brother David were taken to Sobibor extermination camp. After one day in the camp, he fled with his brother to the nearest forest and together with others fleeing he founded the core of the partisan group. During the war, the group led by Jews who had escaped from the ghettos caught nearby and from Sobibor. The group also included the writer Dov Freiberg.