I doubt we'll ever know why this happened, but murder-suicide is what police are saying.
A very successful school friend of my father did the same thing. Out of the blue we heard that he shot his wife and then shot himself. They were found in bed together. There was no explanation and nothing made sense, but it was without doubt a murder-suicide.
I keep going back to the house that was in the wife's name, and which was recently demolished. Maybe she made that decision on her own, and he had just learned about it. As a man in his mid-seventies, I think he could find it excessive to have to go through all the problems that they experienced with building the house where they were murdered. The house that was demolished is only a couple of blocks from the house that is for sale. They bought it at least a year ago, and only recently put their current house on the market. There must be a reason why they waited at least a year to put the house on the market, and to demolish the house two blocks away. The house activity seems to be the only recent thing that happened in their lives, and if the wife made the decisions without full agreement of the husband, that could have caused him to become so upset that he strangled her. Afterward, he would have realized that his life as a free man is gone, so he took his own life as well.