When were the Red Cross investigations of Nazi Concentration camps held?
The IRC's first and only visit to the concentration camps during WW-II was made on 23 July 1944. This was to Theresienstadt, the model ghetto that was established for just such a purpose. Germany only allowed this visit nine months after the IRC had requested it and that gave them plenty of time to stage the show. The IRC issued a "favorable" report on this visit, and though it was protested, it stood. No follow up was made and the vast majority of these prisoners were transported to Auschwitz.
That was a visit by the Danish Red Cross, not the IRC. At the time Denmark was under Nazi occupation ...