I've just flicked back through the threads in this sub-forum and there doesn't appear to be any thread on this topic. Obviously we know that Littlefinger orchestrated the murder through the Tyrells, and that (according to him) the QoT did it. After numerous calculations about the height of the chalice and the table, where exactly everyone was at the time and how the poison was administered we still aren't sure exactly who poisoned Joffrey, how it was done and which Tyrells were involved (though the QoT, Garlan and Margaery would be a good guess IMO). Thoughts? Theories? Speculation? Personally, I've always thought it was Garlan, given that he was sitting beside Tyrion and should have had a good opportunity to put the poison in the chalice. Of course, that may have put Margaery at risk which makes it a little less likely... What do you think?