highest echelons(Generals of Polish Army,highest Civil Servants) involved in taking over houses purchased from those who had murdered or denounced Jewish owners to the Germans.
So your "most important" is ridiculous.

The main element of Polish complicity in the Holocaust is the bitter and pervasive boycott of Jews carried out in the 1930s, as part of the so-called 'cold pogrom'. This left the Jews weakened and dispirited, and enabled the Nazis, when they came, to carry out their roundups much more easily, needless to say with the support of those who had made the boycott in the first place.

is there no collective shame in Poland for past? rehabilitation begins with admission of past. no amount of cleansing otherwise will suffice.