Prisoners were divided into categories. At first, they were classified by the nature of the crime for which they were accused, but eventually were classified by the specific authority-type under whose command a person was sent to camp.:53 Political prisoners who had been arrested by the Gestapo wore a red badge, "professional" criminals sent by the Criminal Courts wore a green badge, Cri-Po prisoners arrested by the criminal police wore a brown badge, "work-shy and asocial" people sent by the welfare authorities or the Gestapo wore a black badge, Jehovah's Witnesses arrested by the Gestapo wore a violet badge, homosexuals sent by the criminal courts wore a pink badge, emigrants arrested by the Gestapo wore a blue badge, "race polluters" arrested by the criminal court or Gestapo wore badges with a black outline, second-termers arrested by the Gestapo wore a bar matching the color of their badge, "idiots" wore a white armband with the label Blöd (Stupid), and Jews, whose incarceration in the Dachau concentration camp dramatically increased after Kristallnacht, wore a yellow badge, combined with another color.:54–69
Smith was told by the former inmates of Dachau that "many ambitious projects were undertaken, such as the production of artificial pepper, the evaluation of seasoning mixtures, the extraction of Vitamin C from gladioli and other flowers, the potentiation of plant growth by hormone-enriched manure, and of most importance to Germany, the development of synthetic fertilizer. As a profitable sideline, garlic, malva, and other medicinal plants, and vegetable seeds, were cultivated by the prisoners and then sold; the profits went to the SS."
The workers who constructed the original buildings were housed in camps near Fallingbostel and Bergen, the latter being the so-called Bergen-Belsen Army Construction Camp. Once the military complex was completed in 1938/39, the workers' camp fell into disuse. However, after the German invasion of Poland in September 1939, the Wehrmacht began using the huts as a prisoner of war (POW) camp.