The destruction of the extermination camps, the cremation of bodies, and the excavation and cremation of shooting victims over the course of 1942-43/44 was constellation of different factors that aligned that pushed the Germans towards this aspect of the Holocaust.

One of the rationales behind the implementation of cremation at the Reinhard camps was practical. The large stacks of buried bodies was both a health hazard and impeded the ongoing operation of mass murder. As the bodies decayed, they created both noxious odors, attracted vermin, and polluted the water. This posed an ongoing health risk to the guards and German occupiers. The stench of death also made it hard to conceal the nature of these camps, which made the process of murdering new arrivals to the camps more labor intensive. Leon Feldhendler, a witness of the killings at Sobibor recounted:

In the first period, there was no crematorium. After gassing, the people were laid into the graves. Then, out of the soil, blood and a bad odor of gas began to surface; terrible smells spread over the whole camp, penetrating everything. The water in Sobibor became rancid.

The problems of Sobibor were similar in many of the other death camps as the summer of 1942 was quite hot and the corpses swelled in the burial pits, spreading disease and creating a noxious environment. These early cremations used both coke fuel and wood for fuel, but were inefficient.

The solution to the SS's problem came from a number of sources. Himmler had tasked SS Standartenführer Paul Blobel in early 1942 to eliminate all traces of mass execution in the Soviet Union. The operation, codenamed Sonderaktion 1005, sought to find the ideal and practical technical solutions to the problem of mass disposals. Blobel's team experimented with various methods at Chelmno and eventually found the ideal method was to stack alternating layers of bodies and fuel connected by railway ties. One particularly gruesome discovery of Sonderaktion 1005 was that human bodies acted as their own fuel, provided they were efficiently stacked. Yechiel Reichman, a Jewish inmate at Treblinka testified postwar:

The SS “expert” on bodyburning ordered us to put women, particularly fat women, on the first layer on the grill, face down. The second layer could consist of whatever was brought—men, women, or children— and so on, layer on top of layer. . . . Then the “expert” ordered us to lay dry branches under the grill and to light them. Within a few minutes the fire would take so it was difficult to approach the crematorium from as far as 50 meters away. . . . The work was extremely difficult. The stench was awful. Liquid excretions from the corpses squirted all over the prisoner-workers. The SS man operating the excavator often dumped the corpses directly onto the prisoners working nearby, wounding them seriously.

Feldhendler similarly testified that the open-air cremations came from the problems of mass burial, which

forced the Germans to build a crematorium. It was a large pit with a roaster above it. The bodies were thrown on the roaster. The fire was ignited from beneath, and petrol was poured on the corpses. The bones were crushed into ashes with hammers.

This lesson that the disposal process was more efficient with more bodies became very important for camps with more permanent crematoria.

Both Dachau and Buchenwald had already installed their own crematoria in 1939. Although not death camps, these unhygienic conditions and general brutality created a large number of deaths among the inmates. The SS had previously farmed out these corpses to local crematoria, but the scale overwhelmed these local businesses and the SS realized that these corpses posed a public relations problem. The SS subcontracted out to two private contractors, Heinrich Kori GmbH and Topf & Sons, to create efficient crematoria suitable for mass burnings. Primarily utilizing coke for fuel, these crematoria used a variety of existing and novel technologies to recirculate heat. As Blobel and his team discovered, human bodies could act as their own fuel and their experience disseminated back through the SS's camp administrators. For example, Auschwitz's crematoria teams would mix fat and emaciated corpses together to create an even heat. The Germans constructed these permanent crematoria at the larger KL work camps and at Auschwitz-Birkenau, which began as a mass-labor camp but transitioned into a hybrid work-extermination camp as the Operation Reinhard camps wound down their operations. Kori and Topf also developed portable oil-fired ovens that could be sent to the areas needing quick disposal.

But permanent facilities also came with a liability in that they were direct evidence of violations of human rights. The Allies had formed the United Nations War Crimes Commission (UNWCC) in October 1942 which had begun to collect evidence of various war crimes and define and delimit the nature of Axis war crimes. The UNWCC kickstarted a process of examining existing treaties of international law and established that German legislation that allowed for such crimes was legally invalid because they violated international norms. The London International Assembly of the UNWCC in mid-1942 claimed that "covering their crimes under a cloak of apparent legality should not help the Nazis to escape justice or that mere terminology or technicalities should not obscure the main issue." The London International Assembly recommended that not only was the Axis powers' war-making itself a crime, but other actions of the Axis should be matters of international justice. he idea of a postwar international tribunal became an official policy of the Allied powers with the Moscow Declaration of October 1943. The Declaration's Statement on Atrocities claimed that the evidence of German war crimes was overwhelming and

those German officers and men and members of the Nazi party who have been responsible for or have taken a consenting part in the above atrocities, massacres and executions will be sent back to the countries in which their abominable deeds were done in order that they may be judged and punished according to the laws of these liberated countries and of free governments which will be erected therein.

But the Moscow Declaration went a step further than just promising punishment for existing war crimes and noted that "the above declaration is without prejudice to the case of German criminals whose offenses have no particular geographical localization and who will be punished by joint decision of the government of the Allies." In short, the Moscow Declaration claimed that some German crimes were so vast and unprecedented they necessitated an international court system to be prosecuted.

But the Germans did not need the Moscow Declaration to understand that evidence of crimes was a liability. The Germans themselves had exploited the Katyn Massacre in its propaganda when it uncovered evidence of the Soviet shootings of Poles in the wake of Barbarossa. The Third Reich had publicized the Katyn massacres as an example of Communist barbarity and thus became acutely aware that the bodies still remain after their murder. Erasing the bodies erases the evidence of the crime. The lack of physical evidence would thus protect the SS, and by extension, Germany, from being held morally responsible for genocide. Himmler likely conceived of cremation as a means to dispose of masses of corpses on a tour of the front in the summer of 1942, and his desire to conceal the crime dovetailed with the hygienic and practical reasons pushing cremation in the Reinhard camps. By the time it was in operation, Sonderaktion 1005's main goal became to eliminate those areas that might be overrun by the advancing Red Army in Belarus and the Ukraine. Around the summer of 1943, the Reinhard camps began to run out of Eastern European Jews to murder, the SS authorities likewise excavated bodies from much earlier mass killings, dismantled equipment, and planted trees over the sites. But by this time But the growing sophistication of the extermination equipment made it harder to conceal and dismantle. Majdanek, which was a subsidiary camp for the main Reinhard camps, continued killing operations of leftover Jews in the General Government and Baltics, was captured nearly intact by Soviet troops in July 1944. The Soviet publicizing Majdanek's gas chambers and crematoria only reinforced the desire to conceal the remaining killing sites like Auschwitz II.

But beyond these practical and exculpatory reasons, the Germans themselves were divided over what should be done with the corpses of their victims. Odilo Globocnik argued to his superiors and colleagues that cremation implied guilt and that the Reich should instead construct vast ossuaries for Jews emblazoned with bronze tablets congratulating his generation for having the courage to see this difficult task through. Despite the fact that some of his superiors agreed with Globocnik's sentiments, including Hitler himself in one account, the Reich's leadership elected to destroy the majority of the Holocaust's corpses. But there still was an uneasy tension between the desire to cover-up the murders and the fact that the cover-up implied guilt. Himmler's infamous Poznan speech in 1943 encapsulated this tension when he noted:

One can consider at a much later time whether the German people should be told more about this. I think it is better that we – we as a whole – have carried this for our people, have carried the responsibility (the responsibility for a deed, not just for an idea); and then we will carry this secret to our graves.

Himmler reaffirms that his SS men will follow orders and may have to carry knowledge of their actions to their graves, but also notes that someday Germans, and by extension the rest of the world, will know what they have done.