CHARGE No. 6 […] The German authorities acting under the authority of Governor General Dr. Hans Frank established in March 1942 the extermination-camp at Treblinka, intended for mass killing of Jews by suffocating them in steam-filled chambers. […] In March 1942, the Germans began to erect another camp “Treblinka B” / in the neighbourhood of “Treblinka A”/, intended to become a place of torment for Jews. […] Late in April 1942, the erection of the first three chambers was finished in which these general massacres were to be performed by means of steam.
“Trial of the Major War Criminals Before the International Military Tribunal”, Document 3311-PS, 1945