In the last months of Hitler’s Reich, as the German armies retreated, the Nazis began marching the prisoners still alive in the concentration camps to the territory they still controlled. The Germans forced the starving and sick Jews to walk hundreds of miles. Most died or were shot along the way. About a quarter of a million Jews died on the death marches.

Although the composition of the ground, largely sand, was favorable for ground-penetrating radar, the dense forest surrounding the site interfered enough with the radar signals that they decided to try another tack. Paul Bauman and Alastair McClymont, geophysicists with Advisian WorleyParsons, a transnational engineering company, had more luck with electrical resistivity tomography, or ERT, which was originally developed to explore water tables and potential mining sites. ERT technology sends jolts of electrical current into the earth by way of metal electrodes hooked up to a powerful battery and measures the distinctive levels of resistivity of different types of earth; the result is a detailed map to a depth of more than a hundred feet.
Historians are divided about the motivations of the members of these mobile killing units. American historian Christopher Browning described one such unit, Police Battalion 101, as ordinary men in extraordinary circumstances in which conformity, peer pressure, careerism, obedience to orders, and group solidarity gradually overcame moral inhibitions. American writer Daniel Goldhagen viewed the very same unit as “willing executioners,” sharing Hitler’s vision of genocidal anti-Semitism and finding their tasks unpleasant but necessary. The diversity of the killers has challenged Goldhagen’s view that the motivation was a distinct form of German anti-Semitism. Yet both Browning and Goldhagen concurred that none of these killers faced punishment if he asked to be excused. Individuals had a choice whether to participate or not. Almost all chose to become killers.
^ Browning i, Christopher (2007). The Origins of the Final Solution: The Evolution of Nazi Jewish Policy, September 1939 – March 1942. U of Nebraska Press. "In a brief two years between the autumn of 1939 and the autumn of 1941, Nazi Jewish policy escalated rapidly from the pre-war policy of forced emigration to the Final Solution as it is now understood—the systematic attempt to murder every last Jew within the German grasp.
Jewish deportees in the Drancy transit camp near Paris, France, in 1942, on their last stop before the German concentration camps. Some 13,152 Jews (including 4,115 children) were rounded up by French police forces, taken from their homes to the "Vel d'Hiv", or winter cycling stadium in southwestern Paris, in July of 1942. They were later taken to a rail terminal at Drancy, northeast of the French capital, and then deported to the east. Only a handful ever returned. #
In October 1941, Himmler authorized SS General Odilo Globocnik (SS and police leader for the Lublin District of the Generalgouvernement) to implement a plan to systematically murder all Jews residing in the Generalgouvernement. In 1942, this project received the code name "Operation Reinhard" (Einsatz Reinhard), a reference to Heydrich (who had been authorized to manage the implementation of the "Final Solution" and who was assassinated by Czech agents in May 1942 in Prague).
While these massacres were happening, the Nazis elsewhere were laying plans for an overall 'solution to the Jewish question'. Death camp operations began in December 1941 at Semlin in Serbia and Chelmno in Poland, where people were killed by exhaust fumes in specially modified vans, which were then driven to nearby sites where the bodies were plundered and burnt. 250,000 Jews were killed this way at Chelmno and 15,000 at Semlin.
The outbreak of war and the invasion of Poland brought a population of 3.5 million Polish Jews under the control of the Nazi and Soviet security forces,[14] and marked the start of a far more savage persecution, including mass killings.[6] In the German-occupied zone of Poland, Jews were forced into hundreds of makeshift ghettos, pending other arrangements.[15] Two years later, with the launch of Operation Barbarossa against the USSR in late June 1941, the German top echelon began to pursue Hitler's new anti-Semitic plan to eradicate, rather than expel, Jews.[16] Hitler's earlier ideas about forcible removal of Jews from the German-controlled territories in order to achieve Lebensraum were abandoned after the failure of the air campaign against Britain, initiating a naval blockade of Germany.[7] Reichsführer-SS Heinrich Himmler became the chief architect of a new plan, which came to be called The Final Solution to the Jewish Question.[17] On 31 July 1941, Reichsmarschall Hermann Göring wrote to Reinhard Heydrich (Himmler's deputy and chief of the RSHA),[18][19] instructing Heydrich to submit concrete proposals for the implementation of the new projected goal.[20]

Germany invaded Norway and Denmark on 9 April 1940, during Operation Weserübung. Denmark was overrun so quickly that there was no time for an organized resistance to form. Consequently, the Danish government stayed in power and the Germans found it easier to work through it. Because of this, few measures were taken against the Danish Jews before 1942.[157] By June 1940 Norway was completely occupied.[158] In late 1940, the country's 1,800 Jews were banned from certain occupations, and in 1941 all Jews had to register their property with the government.[159] On 26 November 1942, 532 Jews were taken by police officers, at four o'clock in the morning, to Oslo harbour, where they boarded a German ship. From Germany they were sent by freight train to Auschwitz. According to Dan Stone, only nine survived the war.[160]

The Sturmabteilung (S.A., Storm Troopers), a grassroots organization, helped Hitler undermine the German democracy. The Gestapo (Geheime Staatspolizei, Secret State Police), a force recruited from professional police officers, was given complete freedom to arrest anyone after February 28. The Schutzstaffel (SS, Protection Squad) served as Hitler’s personal bodyguard and eventually controlled the concentration camps and the Gestapo. The Sicherheitsdienst des Reichsführers­SS (S.D., Security Service of the SS) functioned as the Nazis' intelligence service, uncovering enemies and keeping them under surveillance.
Entering conquered Soviet territories alongside the Wehrmacht (the German armed forces) were 3,000 men of the Einsatzgruppen (“Deployment Groups”), special mobile killing units. Their task was to murder Jews, Soviet commissars, and Roma in the areas conquered by the army. Alone or with the help of local police, native anti-Semitic populations, and accompanying Axis troops, the Einsatzgruppen would enter a town, round up their victims, herd them to the outskirts of the town, and shoot them. They killed Jews in family units. Just outside Kiev, Ukraine, in the ravine of Babi Yar, an Einsatzgruppe killed 33,771 Jews on September 28–29, 1941. In the Rumbula Forest outside the ghetto in Riga, Latvia, 25,000–28,000 Jews were shot on November 30 and December 8–9. Beginning in the summer of 1941, Einsatzgruppen murdered more than 70,000 Jews at Ponary, outside Vilna (now Vilnius) in Lithuania. They slaughtered 9,000 Jews, half of them children, at the Ninth Fort, adjacent to Kovno (now Kaunas), Lithuania, on October 28.

Almost all Jews within areas occupied by the Germans were killed. There were 3,020,000 Jews in the Soviet Union in 1939, and the losses were 1–1.1 million.[400] Around one million Jews were killed by the Einsatzgruppen in the occupied Soviet territories.[401][402] Of Poland's 3.3 million Jews, about 90 percent were killed.[369] Many more died in the ghettos of Poland before they could be deported.[403] The death camps accounted for half the number of Jews killed; 80–90 percent of death-camp victims are estimated to have been Jews.[394] At Auschwitz-Birkenau the Jewish death toll was 1.1 million;[286][404] Treblinka 870,000–925,000;[405] Bełżec 434,000–600,000;[406][287] Chełmno 152,000–320,000;[407][288] Sobibór 170,000–250,000;[408][291] and Majdanek 79,000.[289]
In 1942, Auschwitz II (Birkenau), originally intended to house slave laborers, began to be used instead as a combined labor camp and extermination camp.[23][24] Prisoners were transported there by rail from all over German-occupied Europe, arriving in daily convoys.[25] By July 1942, SS doctors were conducting "selections" where incoming Jews were segregated, and those considered able to work were admitted into the camp while those deemed unfit for labor were immediately killed in the gas chambers.[26] The arrivals that were selected to die, about three-quarters of the total,[a] included almost all children, women with small children, pregnant women, all the elderly, and all of those who appeared (in a brief and superficial inspection by an SS doctor) to be not completely fit and healthy.[28][29]