i think he was murdered by Ay and then Ay forced tuts wife to marry him so he could become king.

Well, and now we can see that he wasn't murdered... What could cause that severe infection in his leg? Did he break it?

The results of the CT were never meant to prove any type of death--only that he did not have a blow to the back of the head that killed him. I'm sure there was a conspiracy of some sort, and he was more than likely murdered in some way, but death did not occur from a blow.
The jury's take on the broken thigh, Neith, is split almost 50-50 on if the break occurred before death, or was the result of Carter and Co.'s "enthusiastic" removal of the body to get at the jewels he wore. IF it did occur before death, it must have been a severe facture, and the broken bone pierced the skin. This is the only way it could have become infected.