That's interesting... He must have been a suspect for awhile then...
If they tracked him closely he must have discarded the murder weapon immediately after the carnage. I would check local dumpsters and POSSIBLY where those dumpsters were emptied, along with local brush/bush locations. Monumental task and they’ll probably never find the knife.
The had an image of his white Hyundai from near the scene.
Apparently, his father traveled (flew?) out to Idaho and the two drove the car back to PA together.