I just had to bring this post from thread 4 forward from
@MassGuy he totally called it that the sheath was left behind.
Post in thread 'ID - 4 University of Idaho Students Murdered - Moscow #4'
ID - 4 University of Idaho Students Murdered - Moscow #4
I linked the wrong post, but here is the post I was referring to:
That's very specific, especially considering there are numerous manufacturers of "combat style" knives.
If it's true they were in fact searching for that brand, then the sheath being found makes the most sense to me.
That would have been a massive mistake on the killer's part, as in addition to purchase records potentially helping the investigation, it would probably be a great source of touch DNA.