I was just thinking.. I wonder if they have SIGNAL STRENGTH DATA from either the cell tower or his phone during his hour-long drive to the south to (presumably) dump the knife.
Because if they do, they can see where the signal strength was STATIC for a minute or so versus where the road is not windy, etc. If they have this data, then they could greatly reduce the areas by the road where he would most likely have tossed the knife.
But bottom line, IMO, they do not need the knife to get a conviction.
They probably also have GPS (not yet mentioned to us at all, but I believe BK carried a smart phone).
I believe he was using a map app in his car, which had to use GPS and therefore, he was tracked by GPS as well. GPS is not turned off by turning off location services.
So there should be TWO sources of evidence for when he stopped or slowed down. We know he turned off the main road and went into Genesee, then reversed course and back onto the main road (etc).
I totally believe they can narrow down where he might have stopped. Still will be hard to find the evidence at this date if, for example, it was weighted in a duffled and tossed into the Snake River at Clarkston. This would mean he may even have gone home to get the right evidence disposal stuff.
He then checked on the King Road house, satisfying himself that no one was even aware of the crime at the time he set out to dispose of evidence.
This might mean that he had gone out a few times before, hunting for humans, but his nerve failed until that particular night. He might not have been as prepared as he should have been - or that we think a smart murderer would be.
Still, if he managed to dump his stuff into the Snake River (better than Latah Creek, obviously; he followed along the Potlatch River and some other bodies of water on his route. Some of them have fish guards further down stream, but if he managed this part of his crime properly, that duffle bad is in sludge at the bottom of one of the rivers.
In checking out his routes, it occurred to me that his first circuit (through Uniontown, I think), did not take him near any major bodies of water - which he might have hoped would happen. So he revises his plan, does NOT turn off his phone, goes home, goes to Moscow, then heads out toward some major rivers. With his phone on. Likely also using Google maps. Panicked beyond any panic he's ever known in his life, because while he's used to getting away with (minor) things like being obnoxious, he has messed up beyond any prior mess-up.