Assassinate
 

I don't think assassinate is working quite right. In the code its setup for a max level of 45, iirc it should be 46. Also there is the bit about the mob being not being engaged for it to trigger which isn't the case. If that were the case the only way for a rogue to assassinate would be to be the puller. I remember assassinating mobs anytime during the fight and I was rarely pulling. I believe there was a racial restriction that the mob had to be a humanoid though.

creature min lvl is 45, has to be humanoid, and you have to be a minimum lvl of 65 in order for you to get the chance to land an assassinate. And indeed, on live servers, its any time you hit backstab, not JUST if you are the puller, and that is the first attack made.