There could be other other exceptions, too, of course, IMO. Specifically, in this, as in many violent acts that otherwise may seem senseless, isn't the rule of thumb "Follow the money" ? In this case there appears to be a great deal of money, including borrowed money, that is basically untethered at the moment, and has arguably been in free fall for some time, IMO. Several prominent clues have been planted, IMO, by MSM that could prove interesting in retrospect. MOO.
I agree this does not appear to be either a rookie murder or a crime of opportunity. The "thrill kill" fall back position doesn't hold water either, IMO, with the limited usefulness of providing an explanation in the absence of facts. MOO.