Neither of whom searched the vehicle. The clerk would have no reason to leave her till and the constable was ok with just letting them drive through into town to just get gas. Did the constable note them returning his way to leave the town after getting the gas? What would that take, 20 minutes max? These were two utter, complete strangers to him as he's used to only checking on local people he knows, and yet he's not alarmed? Tells none of his buddies (would be a big talking point in a small community I'd say) until he's questioned by rcmp? Not much good then, asking him if any other strange car passed his way that day.
I guess, in the court of public opinion we can decide that these two kids are guilty of more than the sole present evidence proves - that of driving a stolen vehicle, as we each choose which witnesses we believe, mostly to fit our own bias. Half a battalion can be re-deployed on a witness casual claim of seeing two guys in a dumpster, but an eye-witness (capable of completing a face sketch) to an argument at the original killing site is dismissed. The last known person to see the victims is kind of important, you'd think. Not surprising then that the rcmp are closing the case at this point: they have their men, so long as no-one is allowed to ask any more awkward questions. And, if they do, let's join websites and label them as conspiracy freaks.
In a court of law, most of these witness accounts would be shredded, as the truth is pursued.