When I read the girlfriend’s name, that was the first thought that came to mind. However I was thinking it was someone from the girl’s family who would have done it, rather than she herself.
I know the police aren’t looking for suspects and are calling it a murder-suicide but I was thinking that perhaps Mrs McNair got fed up with his affair and capped him (in which case I say, Go Mrs McNair.) I just hope he left their 4 sons well provided for. What is it with these married men??