I’ve always believed this was a crime of passion, and that BM actually wasn’t a terrible guy before this event. The thing stopping him from owning up to this, is that he’s managed to justify it in his mind.
I think she learned something about an extramarital affair, or something financial, and she told him it was over.
Something scared him, enraged him, and caused him to lash out.
I don’t believe for a second that he will get away with this, and I think in the coming months we will see an arrest. I cannot wait for the day.