Okay... So it's not immediately obvious... That means I have to think. I hate it when that happens.
You said that the wife was upstairs sleeping (or at least claimed she was). Why was she sleeping in the middle of the afternoon? I thought about this for a while, and came up with a possible explanation. There was another man, who is not on the list, that was "sleeping" with her. The husband came home and caught them "sleeping". He went berserk and was about to kill them both, but the other man managed to kill the husband first. (Is that it, or do I just have a dirty mind?)
The TOG