The Holocaust, what do i still need to learn?

Hi,

            In my last post i told you every thing that all already know about the holocaust. But, i need to learn so much more so that way my essay will be completely accurate. So here are the questions i need to be answered:

            Why did such a tragic event like the Holocaust even occur?
            What was the thinking behind the holocaust?
            What other ethnic groups besides the Jews were in the holocaust concentration camps?
            How many concentration camps were there?
            How did the German people not know what was happening in there country?
            What was the exact number of people that died?
            What took place in the concentration camps?
           
         As you can see there is so much more i still need to know before i can actually write my essay. if you have any suggestions of what else i still need to learn please tell me.

      Cathy