Both the methods used and the range of crimes 'meriting' execution changed under the Nazis. Dark History says:
When Hitler came to total power, he decided that criminals and enemies of the state should be executed by either guillotining [or hanging from 1942] and he ordered the construction of 20 guillotines.
The guillotine in the Plotzensee Prison execution room. Source: https://ghb67.wordpress.com/2012/04/29/the-guillotine-in-nazi-germany/
Several other sites (here's one) mention the methods used for capital punishment in Nazi Germany. In summary, the three main methods of execution were generally:
- Guillotine, used for criminals (replaced the axe which had been used before Hitler came to power)
- Hanging, used for political enemies
- Shooting, used for political enemies and by the military
Among the crimes which could or did carry the death penalty were
...grave arson, aiding and abetting treason, betraying a secret (mandatorily), procuring a secret for the sake of betraying it, insidious publishing or rhetoric, failure to denounce a capital crime, destroying means for military use, sabotage(mandatorily for soldiers), kidnapping (mandatorily).... a "dangerous habitual criminal" or one convicted of rape...
and so on.
What I can’t find out is why the guillotine was used for criminals and (usually) hanging or shooting for political enemies. The guillotine seems more merciful than hanging, so it seems the Nazis regarded political enemies as worse than murderers, rapists, e.t.c. – but this is just a guess based on little evidence.
Are there any documents, or were any statements made, explaining the reasons for the methods of capital punishment used for different kinds of prisoners? Wikipedia quotes Hitler saying capital punishment is a deterrence, but there is nothing on the methods.
An exception was made for the six members of the White Rose anti-Nazi resistance organization, who were beheaded in 1943.
Why was this exception made for the White Rose movement?