Someone pointed out, on another site, the timing of the killing is odd if a targeted hit. Why not wait until Jan 1st, or the weekend when Spencer would be off work, and not missed, giving more time between event and discovery? Was it someone who wanted the kids to be found right away, to be safe and not alone? So, so many questions.
And if they were tracking or watching the family or a family member, maybe they knew they’d be out of town or have plans for 12/31-1/1? Not sure if they actually did, but it’s very possible.