Agreed there is hopefully more that justifies that level of specificity. 2011-13 Elantra (4 Dr sedan) is quite specific, even if tens of thousands were imported.
I do have concerns it may be over specific, as in some Hyundai dealership said, "yeah that looks like a 2011-13 Elantra" without realizing a Kia Forte is extremely close and nearly the same car sans badges and some minor sheetmetal details.
Everyone in a 3 state area is looking for an Elantra, when it's corporate doppelganger (Kia) may be right under their noses.
If they're not getting good leads maybe it's time to open up that search a bit. i.e. "older white Hyundai or Kia 4dr sedan" and see what turns up within an yours drive in all directions. Probably closer unless it was a complete random or SK.
Let's say it was an occasional customer at a place where one of the victims worked. Let's say the bar. How far would you drive for a couple of beers? Especially these days. 10 miles? Maybe 20 miles since it is sort of out in the middle of nowhere. 30 tops. How far do semi-regulars live from a bar? 5 miles maybe?
Pull up a map of Idaho. Draw a rough circle from Palouse or Potlatch down to Lewiston, Troy or maybe Deary on the east to Pullman or a bit further west. Go much beyond that and it's starting to be a hike for more than an occasional jaunt. Especially when the weather turns. If it's not a student or complete anomaly, I'd bet the killer lives within that area. Otherwise that's a serious hike to risk a go in, kill 4 people, and drive an hour back home at 0400 type plan. Especially if it was a drunken rage type thing.
I think it was a local, student or 20-35 y/o resident within 10 miles of town.
As always, moo.