IMO, there are already too many things lined up that a reasonable person would not convict.
BK's DNA on the knife sheath was a home run. Getting any VICTIM'S DNA from the Elantra or his apartment would be a grand slam...game over.
Others on here have said and I agree, that this so much more circumstantial evidence with the car, license plate absence, phone cell tower pings, social media messages (possibly), (possibly) searches on his phone or computer relating to any of the girls.. that this alone COULD have been but was not probably quite enough to ensure a conviction.
Bottom line is LE got their guy and with all the help from Idaho State Police and the FBI, they will have all their ducks in a row come trial time.
I am not sweating this...