I think Ay did, but it's suspicious that Horemheb made his lifelong goal to erase all records of Tutankhamen .

I also definitely don't think that Ankhesenamun did because why would she, really? She seemed like such a loving wife AND she knew that she probably would be forced into marrying someone old like Ay. The only reason ppl think she's a major suspect is because she was with Tut all the time, and therefore would have been able to sneak up on him and know his weaknesses. Even so, I firmly believe that Ankhesenamun was not the murderer. And who knows, the recent evidence that points to King Tut in fact NOT being murdered, rather dying of an infection in a broken leg might be true. I don't know, I personally believe that he was murdered more because it is interesting AND Ay did seem to really want to take over the throne. But whatever the case was, I do staunchly believe (and hope) that it was NOT Ankhesenamun.