The 4 questions for Tisha B'av

The 4 questions for Tisha B'av

  לז"נ הקדוש ר' משה פרידמן הי"ד 

   נעקד"ה  ג' אב ע"י הגרמנים הארורים ימ"ש                                                                                                                              

The Bais Hamikdash was destroyed because of Kamtza and Bar Kamtza. (Gittin 55b)

1) Why was Kamtza at fault?

2) Why wasn’t the Ba’al Haseudah at fault ?  Shouldn’t he be the number one culprit ?

3) Why were the Rabonon who kept quiet at the meal not at fault, 

4)The Gemoro on 56a said it was R. Zecharia ben Avkulas fault. 

So whose fault was it?