Oh something I can answer confidently!

So I want to clear something up really quick before I get into it: a lot of Germans (I'd say most, actually) did know about atrocities being committed, they didn't necessarily know about the specifics. Soldiers on the front wrote letters home, and in those letters they'd often write about things they'd taken part in or witnessed. Soldiers on leave would talk about it to friends and family. These guys were often talking about mass murders happening in forests in the East, and special groups (what we know to be the Einsatzgruppen) coming in to search conquered areas for Jews. These stories spread all throughout Germany, but the general feeling about them was that they were individual events, rather than part of something bigger. Regarding the camps, people knew they were bad. The gas was kept secret to a very large extent, but people knew about the camps. Especially towards the end of the war, prisoners would moved from camp to camp in death marches, and these marches oftentimes took them through towns where civilians would see them and their condition.

They likely did not know about forced sterilization of certain groups like the so-called "Rhineland Bastards" (half black Germans in the Ruhr valley, children of French colonial soldiers). Same goes for medical experiments. Those were kept secret, particularly the sterilization of the "Bastards". That information only came to light in 1979 with the publication of research done by German historian Reiner Pommerin.

So generally I just wanted to make it clear that a lot of Germans did have a sense of what was going on, if only a vague one. The Wehrmacht was much more complicit than people think.

In answer to the question now that we're clear on that

Well first we have to figure out who was in Germany when the war ended. What kinds of people? Generally speaking, there were four or five main kinds: Fraternizers, Victims, Mitläufer, Rubble Women, and the uninvolved.

Fraternizers were the people in Germany who didn't care one way or they other for Nazi policy, but still joined the party or supported the party for personal gain. They were opportunists who were hated in post-war Germany because they knew what was happening was wrong but they actively supported it anyway. One could draw a comparison to collaborators in France, though Fraternizers were often less extreme. In media and literature, Fraternizers are often portrayed as women.

The victims in question were victims of Nazi abuse (camp survivors, stuff like that) or survivors of the mass rape perpetrated by Soviet troops. Lots of Germans identified with the rape victims, turning themselves into victims by proxy.

Mitläufer means "with-walker" or rather, "someone who walks with". These were people who could've helped to prevent or stop some of the evils being perpetrated, but didn't. There's a very good film called "The Murderers are Among Us" that was created in 1946 in the Soviet zone of Germany that goes over this. The main character is a Mitläufer. He had been a doctor in the Wehrmacht, and on Christmas Eve, his commanding officer ordered the murder of 120 Polish civilians. The doctor basically says, "We don't have to do this, it's Christmas!" and the officer basically calls him soft and orders him to get a star for the tree and he does. German audiences in 1946 interpreted this as, "the doctor tried to stop it but couldn't. It's all the officer's fault." What the director, Wolfgang Staudte actually intended was that the doctor didn't do much of anything to stop it, so he's complicit as well. Mitläufer were also hated, but once historical revisionists started to warp people's understanding, the blame was shifted almost entirely to the Nazi party and away from the Wehrmacht/individual.

Rubble women would clear the streets of rubble in the aftermath of the war, and became a sort of symbol for Germany's future. Instead of destroying, they were repairing, and they were very literally clearing the path. They can actually be seen in the aforementioned film, and they're real too! It was pretty much all filmed in the actual rubble of Berlin.

The other category was more complex. There were those who were lucky enough to have nothing to do with the war, but they were few because in a total war the entire nation is mobilized in one sense or another. There were veterans who weren't Mitläufer, and plenty of people who weren't Fraternizers or victims.

So in effect Germans themselves were vilifying Mitläufer and Fraternizers, a trend that would increase stigma against Nazis and sympathizers.

From a legal standpoint, the American sector attempted to reprimand every Nazi they found, restricting their opportunities and sometimes even jailing them. The Americans found out quickly that there were far more many Nazis in their sector than anticipated. It became too unfeasible and was given up. The British and French sectors also saw little success in reprimanding every Nazi. The Soviets had the most interesting take on it. They blamed it all on the capitalist Germans of the other 3 sectors. Compared to the other sectors the Soviets apprehended very few Nazis. Something else that they did was to not rebuild certain things. In other parts of Germany famous buildings or landmarks that had been damaged by the war were rebuilt, but in Dresden for example, the Frauenkirche (famous cathedral) laid in rubble for the entire existence of East Germany.

Tl;Dr -- German public opinion turned against Nazism, and by association against all the Mitläufer and Fraternizers. False feelings of victimhood held by people who weren't really victims led to the idea that people had been manipulated, that they didn't want to do these things or approve of these things, but had no option. It was a sense of unearned exoneration, which in turn shifted their guilt to Nazi leadership and the direct perpetrators.

Sources:

Peter Fichte, Life and Death in the Third Reich

Ulrike Weckel, "The Mitläufer in Two German Postwar Films: Representation and Critical Reception," History and Memory 15, no. 2

Wolfgang Staudte, The Murderers are Among Us

Elizabeth Heineman, "The Hour of the Woman: Memories of Germany's 'Crisis Years' and West German National Identity," The American Historical Review 101, no. 2