At the start of the Second World War, Adolf Hitler and Heinrich Himmler agreed that selected “enemies of the nation” should be executed in concentration camps, outside the regular legal channels. Killing these “enemies” inside camps promised the “swift justice” Nazi leaders had dreamt about. Their thinking was outlined in instructions by Himmler’s deputy Reinhard Heydrich to regional and district Gestapo headquarters on 20 September 1939.
[…] Every attempt to undermine the solidarity and the fighting commitment of the German people must be ruthlessly suppressed and severely punished. […] In each case a distinction must be made between those who can be dealt with in the normal way and those who must be subjected to special treatment. In the latter case we are dealing with behaviour which is of such iniquity, which poses such a threat, or has such a propaganda effect that it deserves to be eliminated by the most ruthless action (through execution) without consideration of the person involved. Such cases are, for example, attempted sabotage, the incitement or subversion of the army or of a large group of people, the hoarding of large quantities of goods, participation in Communist or Marxist activities.
Source: Bundesarchiv Berlin, R 58/243, Bl. 215
Translation: Lesley Sharpe and Jeremy Noakes