The worst was in the ruins of Warsaw, or the fields of Treblinka, or in the marshes of Belarus, or the pits of Babi Yar

The American and British soldiers who liberated the dying inmates from camps in Germany believed that they had discovered the horrors of Nazism. The images their photographers and cameramen captured of the corpses and living skeletons at Bergen-Belsen and Buchenwald seemed to convey the worst crimes of Hitler. As the Jews and Poles of Warsaw knew, and as Vasily Grossman and the Red Army soldiers knew, this was far from the truth. The worst was in the ruins of Warsaw, or the fields of Treblinka, or in the marshes of Belarus, or the pits of Babi Yar.

T. Snyder, Bloodlands (2010), 311-2

There's more on this around 382f. He is very good on uncovering our historiographical bias on this.