Economic needs and the prolonging of the war established the need to utilize the Jews as a labor force. Six Extermination Camps I n Chelmno, the first extermination camp to be established with the single purpose of killing people — first of all Jews — in a systematic fashion,inmates were gassed to death using exhaust gas from trucks, in the period of December Marchand again from June-July Criminals were marked with green inverted triangles, political prisoners with red, "asocials" including Roma, nonconformists, vagrants, and other groups with black or—in the case of Roma in some camps—brown triangles.
Concentration camps also existed in Germany itself, and while they were not specifically designed for systematic extermination, many of their inmates perished because of harsh conditions or they were executed.
In some camps, Nazi doctors performed medical experiments on prisoners. Homosexuals were identified with pink triangles and Jehovah's Witnesses with purple ones. There were also large numbers of Romani people, ethnic PolesSerbspolitical prisonershomosexualspeople with disabilities, Jehovah's WitnessesclergymenEastern European intellectuals and others including common criminals, as the Nazis declared.
Murder operations began there on December 8,and continued intermittently until January