One potentially but as of yet unmentioned aspect is the "game thing" itself. The fact that he refers to this as a "game," indicates that by means of some conspiracy theory site or other, he was more or less interacting with others in competitive harassment.

Take the following potential scenario:

  Impressionable youth joins conspiracy site, finds lots of anti-semitic information. 
  The youths of the forum are encourage to pick a Jew and harass them, recording both their creations (i.e. a plastic container filled with ashes), and the responses of the person they are harassing.
  Within the context of a game this harassment can immediately seem quite harmless. I am actually not thinking much about the person who is on the receiving end of my "prank" anymore, I am simply thinking of the optimal reaction I can get from my "innovative" creation in the harassment sector. 

  Anyways, easy to see how something like this could get out of hand. Very out of hand in this case.