There was no evidence around the tent area of anything unusual, such as a puddle of frozen blood. If the tent didn't hold up that night and they froze to death down at the tree area, there's no major issue, in terms of making sure the evidence is preserved in some sort of perfect, idealized way (that's what I'd guess they would have been thinking, as it is something I would guess most people today would think who weren't trained in investigative techniques). They could not predict that after circa 2000, it would appear on internet lists of "great mysteries" and "disturbing incidents," and perhaps if they could, they would have had a good laugh and drunk more vodka!