The German military attaches reported the murders of the millions in the Ukraine, and set the stage for the murder of six millions Jews and millions of other "undesirables" by the Nazis... continuing the pioneering work of the Socialist vanguard, the USSR, in the 1930's
The military cooperation between Germany and the Soviet Union ended quite early in Hitler's rule, between May and October 1933. Sebastian Haffner describes how in his book Der Teufelspakt: Die deutsch-russischen Beziehungen vom Ersten zum Zweiten Weltkrieg (pp. 131-2).
Haffner's words, published in 1988, were confirmed by the Soviet documents later revealed and published in Yuri Djakov & Tatyana Bushuyeva, The Red Army and the Wehrmacht: How the Soviets Militarized Germany, 1922-33, and Paved the Way for Fascism.