Part 1/3

I have written several answers on this topic here, here, and here and from these answer:

First off, it is important to take a look at the Wehrmacht as an institution of the Nazi state. As such, the Wehrmacht as an institution superseded the "normal" function of an army within your average nation state (this is a bit simplified as neither a normal function or average nation state exists strictly speaking but I mean stuff like defense or fighting a war) and crossed the territory into becoming an institution heavily involved and complicit in the crimes of the Nazi state.

To exemplify (the list I am providing is far from extensive):

• The criminal conduct in the Soviet Union and against Soviet POWs

The probably most famous examples of Wehrmacht crimes are probably the Commissars Order and the Kriegsgerichtsbarkeitserlass. When preparing for the invasion of the Soviet Union, the Wehrmacht leadership in conjecture with the Nazi leadership issued orders that the war in the Soviet Union was not to be treated as a "normal" war but a war of "Weltanschauung", meaning they were not just fighting another country but rather Jewish-Bolshevism itself. To that end, the OKW gave the order that political commissars within the Red Army were not to be treated as POWs but were to be shot immediately after capture. Political Comissar included however not only people who held this position but also any member of the Communist Party of the Soviet Union as well as all Jews. In conjecture with this order, the Kriegsgerichtsbarkeitserlass decreed that no member of the Wehrmacht could be persecuted for any and all war crimes they committed while in the Soviet Union. So rape, pillaging, murder and burning down villages were all fair game for all members of the Wehrmacht. The Commissar Order alone lead to something between 60.000 and 140.000 victims.

Additionally, the Wehrmacht as an institution was responsible for Soviet POWs in general. In that function it was the Wehrmacht which basically let them starve to death in violation of all international treaties and conventions. Basically, the Wehrmacht built POW camps for Soviets by just putting up a fence and putting the POWs in there, letting them starve as a policy before the leadership of Nazi Germany needed them for forced labor in 1942. But even with that the death toll is staggering. Christian Streit estimates that about 3.3 million Soviet POWs or 57% of all Soviet POWs captured by the Wehrmacht died while in captivity.

• The Wehrmacht as an occupational and security force

The Wehrmacht was an important part of the occupation of conquered territory and as a security force in that occupied territory. As such, it committed murder and war crimes. Taking Serbia as a territory that was directly administered by the Wehrmacht, Wehrmacht units shot 20.000 civilians alone in the time frame from September to December 1941 as part of a campaign of retaliation for Partisan attacks. The Wehrmacht commander of said territory, Franz Böhme, instituted a policy of 100 civilians shot for every dead German soldier and 50 for every injured German soldier. The vast majority of victims were not related to the attacks or the Partisans but rather male Jews or Roma and Sinti thus making Serbia the first territory outside of the Soviet Union in which Jews were systematically killed by the German occupation.

Crimes such as these are numerous and extend even into the Western territories of Europe. For example, the Wehrmacht massacre of the Italian village of Marzabotto in October 1944.

Also, as an occupational force, the Wehrmacht was responsible for administering Nazi racial policy in its territories as can be read in detail in Dieter Pohl's book on the Wehrmacht in the Soviet Union.

• The Wehrmacht and the Holocaust

As mentioned above, the Wehrmacht as an institution was involved in the Holocaust in Serbia, where it was Wehrmacht untis who killed the male Jewish population or when it came to Soviet Jewish POWs. But the Wehrmacht also collaborated closely with the Einsatzgruppen in the Soviet Union basically either transferring Jews into the hands of these mobile killing units or even lending a hand when it came to shooting Jews. Additionally, Wehrmacht units in Poland and the Soviet Union also were involved in killing the mentally handicapped and disabled.

Furthermore, the Wehrmacht established Ghettos and provided transport for Jews to be deported to Auschwitz, e.g. in France and aided in registering and confining Jews to certain quarters in countries such as France and Belgium.

The question of how many knew of war crimes and what they knew of them is easier to answer, especially in light of the newer research by Felix Römer as well as Sönke Neitzel and Harald Welzer. They worked extensively with Allied protocols of conversations between German POWs recorded in Allied camps when they didn't think anybody was listening. Their research uncovered that knowledge of war crimes was ubiquitous among members of the Wehrmacht. Every soldier knew of atrocities that had been committed against Jews and other civilians because they had either been present, had participated or had been told about them by their comrades. During their time as POWs, they quite freely discussed these crimes. To exemplify this, Römer cites among others the following exchange between the Viennese Artillerie-Gefreitem Franz Ctorecka and the Panzer-Gefreiten Willi Eckenbach in August 1944 in Fort Hunt (translation my own):

C: And then Lublin. There is a crematoria, a death camp. Sepp Dietrich is involved there. He was somehow caught up in this in Lublin.

E: Near Berlin, they burned the corpses in one of these thingies ["einem Dings], the people were forced into this hall. This hall was wired with high-voltage power-lines and in the moment they switched on these lines, the people in the hall turned to ashes. But while still alive! The guy who was in charge of the burning told 'em: "Don't be afraid, I will fire you up!" He always made such quips. And then they found out that the guy who was in charge of burning the people also stole their gold teeth. Also other stuff like rings, jewellery etc.

[Römer, p. 435f.]

What this passage shows is that these Wehrmacht soldiers, who after all were both on the lower side of the ladder, being only Gefreite (lance corporals) were uncannily well informed even if the story about using electricity for executions wasn't true. But knowing not only of the Majdanek death camp near Lublin but also knowing about Sepp Dietirch's involvement proves them to be very well informed.

Or take this exchange between two Wehrmacht soldiers, Obergefreiter Karl Huber and Pioniersoldat Walter Gumlich, in Fort Hunt:

H: One day, one guy just came and stole this Russian's cow and so the Russian defended himself. And then we had to hang fifty or a hundred men and women and let them hang there for three or four days. Or they had to dig a trench, line themselves up at the edge and were shot so they fell backwards into it. Fifty to a hundred people and more. That were the so-called "retributions". But that didn't help anything. Or when we set the village son fire [...] Partisans were naturally dangerous, we had to defend ourselves against them but this was something different [...]

G: Ach, that were war operations. They [the people who did the above] are not really criminals.

H: Exterminating whole families, shooting their kids etc., literally killing whole families? We are guilty if the military without any right or any order steals the last bread of some farmer.

G: Oh, come on.

H: Ach, don't defend them.

These and so many more conversations of this kind between Wehrmacht soldiers show that virtually every soldiers had either heard or seen these crimes if he had not participated in them himself. And given how numerous the crimes of the Nazis and the Wehrmacht were in the Soviet Union and elsewhere, this is hardly surprising. You already mentioned it in your expanded text above and I go into this in the linked answers but it is imperative to realize that the war against the Soviet Union was planned, conceptualized and fought as a war of annihilation, being in itself basically a huge war crime. Nobody is this fact more obvious than in the OKW's Kriegsgerichtsbarkeit Erlass, which actually forbid Wehrmacht soldiers from being persecuted for war crimes in the Soviet Union. That this was seen as necessary, tells you not just how deeply the Wehrmacht was involved but just what kind of war they planned to fight: One where combat operations and war crimes bled into each other seamlessly.

The background of this is touched upon in my linked answers as well as by Dr. Waitman Beorn in the linked AMA here.