Breitman, Richard; The Architect of Genocide: Himmler and the Final Solution. New York: A. Knopf, 1991, p 202.
After the development of a mobile killing van in the fall of 1941, the device was tested on Soviet POW's in Sachsenhausen, and found completely satisfactory - three more trucks were converted, and initially put to use in the Ukraine. There was, however, an urgent need for them in the Wartheland.
In July one of Eichmann's subordinates had raised the idea of finishing off the Jews in the Wartheland 'in humane fashion,' saying at that time that the idea seemed fantastic but was practical [footnote 67]. An extermination camp in the Wartheland could sweep Jews out of the Lodz ghetto....
...That fall Herbert Lange, commander of the unit that in 1940 had carried out gassings in vans using bottled carbon monoxide, rode around the Wartheland looking for a suitable site for a camp. He found an unoccupied castle along the New River, at a place called Chelmno, thirty-five miles northwest of Lodz, where a camp was established in late October or early November. Nearby was a forest where the gas trucks could operate discreetly. Gassings of Jews from the Wartheland were first carried out on December 8, 1941. Chelmno became, in effect, the first death camp in operation [footnote 68].
. See Ho"pner to Echmann, 16 July 1941, reprinted in Lucjan Doboroszycki, ed., The Chronicles of the Lodz Ghetto 1941-1944. (New Haven, 1984), lii-liii.
. Hilberg, Destruction, I, 212-14.