Not to depart from the seriousness of this case, but sometimes when analyzing a puzzle or problem, it helps to shake things up a bit, step back, and examine things through a dramatically different lens.
In the following example each victim in this case is examined separately. Could the dilemma in figuring out what occurred to the McStays be in thinking of them in the as a unit, four victims, all killed for basically the same reason (natural, as they died together), but if only one person was the target, and the others collateral, maybe isolating their individual circumstances will give a new perspective.
Occam’s Razor Scenario #1:
Man is found murdered, bludgeoned to death, in a shallow grave in the desert, his vehicle and home keys in his pockets. Also a few loose keys to padlocks are found in his pockets as well, keys consistent with padlocks used on storage units. He is currently renovating his home, and has most of his belongings in storage Pods. He is found wrapped in a blanket, tightly packaged with a cord and straps in a shallow grave in the desert, over an hour from his home. His vehicle is found in the parking lot of a strip mall at the border.
His DNA is dominant in his vehicle, beverage containers and his home appears as if no one aside from himself has been there.
If Joseph McStay had been the only victim, what conclusions would the evidence just around his death be?
Would the most obvious conclusion be that this man drove to the shopping mall at the border, there he was abducted after parking his vehicle, taken to another location, most likely a home close by, murdered at this home, wrapped in a blanket from that home, and then driven far from that home to the desert to place the murder as far from the site of abduction and murder as possible?
[For the moment this is leaving out motive and the fact that parking attendants swear the Trooper didn’t arrive to that San Ysidro border until Monday.]