I enjoyed all the conspiracy theories here-some people actually believe all that stuff!
My personal feeling is that the assassination was just some idiot with a gun who wanted to get famous and commit "suicide by cop." Can't be sure though..
  It could have been an  FSB "wet squad" acting on orders from Putin. 
  That Gulin guy is pretty interesting. He reminds me of some of the other froot loop types the US is famous for-and he's rich, too. Not to mention any names.