Some Poles helped Jews risking their own lives, others just blackmailed them for money or jewelery and some murdered to get rid of them and lay hands on their property. The situation of the German occupation made all three options possible. So abstain from ANY occupation. It's just a lection of history.
World Jewish Congress: Nazi train treasures must go to rightful owners (Reuters)
from the article: New case study explores role of Polish peasants in Holocaust atrocities