Perhaps, from the “victim” himself:
(Another angle, we don’t know whether Thompson “had had enough” and planted the seed in his wife’s mind “threats”, and paid the assailant himself, so to go out looking like a victim.)
I have to go with the most likely perp in any homicide without strong evidence leading in another direction—the spouse hired a killer.
Not all hired killers are skilled professionals—it is probably a normal curve of skill level like any other occupation.