So I'm currently reading "A Royal Game" by the Austrian author Stefan Zweig. One of its main characters is imprisoned by the Nazi regime and makes a quick passing reference on concentration camps where "prisoners are physically and psychologically tortured" (he was not imprisoned there and it's not what the story is about, but that's besides the point).

Now, Zweig died by his own hand in 1942, years before the war would end. This novella was published around a year before his suicide in Brasil, far away from home. I could imagine that his correspondence with people in Europe allowed him to know about the camps, and even that seems strange to me (wasn't most of Europe occupied by the Nazis by this point, so it would be heavily censored if it existed at all? His homeland at the very least?).

Even though this might have been a misunderstanding on my part I was under the impression that the average person didn't know about the concentration camps. They did know about the persecution and execution of jews and other minorities, but I didn't know they knew about the camps, I assumed they were top secret (the Allied Soliders who reached the camps where surprised and disturbed to discover them, weren't they?). Even though governments could know about it, there is no reason to believe the average person would know about it, especially not when they're so far away and disconnected from the on-going war in Europe.

So how could he know about it? Did people know about concentration camps?