Here's what I think.
They carefully collected tons of forensic evidence from all over the house, each designated as a different time phase in the crime. They found car carpet fibers on the stairs and on the bedroom floor (using many different vacuum bags and carefully labeling, taking over 4000 pictures of where they gathered this evidence).
They knew a Hyundai Elantra had passed by a Ring cam. So they went into the database of carpet fibers and lo and behold! The fibers on the feet of the alleged killer are from a Hyundai Elantra - but only from 2011-2013.
That Elantra is hidden someplace, IMO. Probably at a remote location, perhaps still with the killer. His family knows he has this car, but is silent (and LE knows who they are, too and are waiting to see if they are going to budge and give up where the car/person driving car might be).
I don't think that Hyundai is still in Idaho, myself. Nor is the killer. But if they find that Hyundai, they will find a person who is definitely worth interrogating.