Bełżec extermination camp
Niemann joined the Nazi Party in 1931 as member number 753,836 and the SS in 1934 as member number 270,600. He first served at Bełżec extermination camp, where he commanded Camp II, the extermination area. He then was transferred to Sobibor extermination camp. Niemann was deputy commander of Sobibor on various occasions in 1942 before being given the position permanently in early 1943. After Heinrich Himmler's visit to Sobibor on 12 February 1943, Niemann was promoted to "SS-Untersturmführer".