Before the 1941 German invasion of the Soviet Union, Nebe volunteered to serve as the commanding officer of Einsatzgruppe B, one of the four mobile death squads of the SS.

Under his leadership, equipped with arbitrary powers of arrest and detention, the Kripo acted more and more like the Gestapo, including the liberal use of so-called protective custody and large-scale roundups of "asocials".

[9] In 1939, Nebe lent a commissioner of his Criminal Police Office, Christian Wirth of Stuttgart, to the Action T4, which ran the programme of involuntary euthanasia (murder) of the disabled.

Nebe volunteered to command Einsatzgruppe B, an SS death squad that operated in the Army Group Center Rear Area as the invasion progressed.

The unit's task was to exterminate Jews and other "undesirables", such as communists, "Gypsies", "Asiatics", the disabled, and psychiatric hospital patients in the territories that the Wehrmacht had overrun.

[19] By August 1941, Nebe came to realize that his Einsatzgruppe's resources were insufficient to meet the expanded mandate of the killing operations, resulting from the inclusion of Jewish women and children since that month.

Murder with carbon monoxide gas, already in use in the Reich as part of the "euthanasia" program, was contemplated, but deemed too cumbersome for the mobile killing operations in the occupied Soviet Union.

One night after a party, Nebe had driven home drunk, parked in his garage, and fallen asleep with the engine running, nearly dying of carbon monoxide poisoning from the exhaust fumes.

[24] To conduct the experiments, he ordered the SS chemist Albert Widmann, a member of the criminal-technical institute of the RKPA, to come to Minsk with 250 kilograms (550 lb) of explosives and exhaust hoses.

[12]Two days later, Nebe and Widmann carried out another killing experiment: five psychiatric patients from Mogilev were placed in a hermetically sealed room with pipes leading to the outside.

Nebe's report dated 9 October 1941 stated that, due to suspected partisan activity near Demidov, all male residents aged 15 to 55 were put in a camp to be screened.

[33] Following the 1942 assassination of Heydrich, Nebe assumed the additional post of President of the International Criminal Police Commission, the organization today known as Interpol, in June 1942.

[35] Also in 1944, Nebe suggested that the Roma interned at Auschwitz would be good subjects for medical experiments at the Dachau concentration camp, after Himmler had asked Ernst-Robert Grawitz, a high-ranking SS physician, for advice.

[38] Martin Kitchen casts Nebe as an opportunist, who saw the SS as the police force of the future, and as an "energetic and enthusiastic mass murderer, who seized every opportunity to undertake yet another massacre."

[40] Headland writes that the reports "bear witness to the fanatic commitment of the Einsatzgruppen leaders to their mission of extermination"; their ideology and racism are evident in the "constant debasement of the victims" and "ever present racial conceptions concerning Jews, Communists, Gypsies and other 'inferior' elements".

Headland concludes that Nebe was an ambitious man who may have volunteered to lead an Einsatzgruppen unit for careerist reasons, to curry favor with Heydrich.

Any misgivings he may have entertained as to the feasibility of the undertaking failed to prevent him from overseeing the murder of close to 50,000 people in the five months Nebe commanded his unit.

[41] Gerald Reitlinger describes Nebe's reasons for joining the Einsatzgruppen as "placation" and a desire to hold on to his position in the Criminal Police Department, where, since 1934, Gestapo men were gaining influence, and which was later taken over by Heydrich.

Reitlinger writes: "If Nebe did in fact retain his office till 1944, it was because of the five months he spent in Russia, or, as his friend Gisevius politely referred to, 'at the front'."

[42] Alex J. Kay writes that "the role, character and motivation of those involved both in planning—and in some cases carrying out—mass murder and in the conspiracy against Hitler deserve to be investigated more closely".

[43] Several apologetic accounts produced by the conspirators behind the 20 July plot described Nebe as a professional police officer and a dedicated member of the German resistance.

[44] A Swedish police official active in Interpol during the war years, Harry Söderman, described Nebe and Karl Zindel [de], a key RSHA figure responsible for persecution of the Roma, in his 1956 book as "professional policemen.... very mild Nazis".

[34] The historian Christian Gerlach, writing about the 20 July conspirators and their complicity in war crimes of the Wehrmacht, calls Nebe a "notorious mass murderer".

[45]Gerlach doubts that Nebe falsified Einsatzgruppe B reports and puts Schlabrendorff's claims in the context of bomb plotters' memoirs and the then-prevalent assessments of the opposition group within the high command of Army Group Center: "Especially with reference to the murder of the Jews, [it is said that] 'the SS' had deceived the officers by killing in secret, filing incomplete reports or none at all; if general staff officers protested, the SS threatened them."