From a common sense standpoint: some bozo hothead gets into a dispute at a party. Who is he going to find as “friends’ who will join him by going back to crazily kill a bunch of people they don’t know?? What on earth would be the motive of such acquaintances who are not part of the underlying dispute? No, I suspect it is more of a plan, perhaps on the shelf but set in motion by some incident today.
Just heard on CBS news (wife is watching) that the working theory is “workplace violence”. That must be code for Sudden Jihadi Syndrome.