I have been here a long time and when cases go “cold” as far as info...the same bizarre theories seem to surface, including cartels, hits, drug money owed, etc...none of which I remember ever being true, as those types of cases seem to be solved quickly...LE knows when people are killed over drug money, debts, etc as they easily enough come across proof. If they don’t know the exact culprit, they know, more or less.
Crimes when the motive is unknown, as this may be, are much harder to solve. I can’t rule out a crime similar to what happened to Holly, just because that happened at such an unlikely time and way, too. Her brother is lucky to be alive. It could have been semi-random in that the perp(s) knew the somewhat isolated house included a teen girl, if that was their goal. The boldness/thoughtlessness of shooting and kicking doors does summon up junkies high on meth, as well as other scenarios that include plain old rage.
Completely random seems unlikely unless the house was also ransacked. We do not know, but the first responder seems to have mentioned nothing that made it sound that way. Jmo