The killer bought one gas can and did not return it but even if she had returned it, so what? She had two others that she borrowed.
I posed the question a while back of who in AZ and surrounding areas has ever taken extra gas along in cans in the trunk, through the desert in June, and no one here admitted they had ever done it or knew anyone who had ever done this. It's stupid because it's not necessary, let alone extremely dangerous.
But even if all of a sudden now with this posting half a dozen people were to post claiming this to be a common practice I say again, so what? Killer Arias took numerous steps in preparation for her trip to slaughter a man in his own home that clearly show premeditation--the gas cans are strong evidence, but certainly not the only evidence the state had. If anything ever gets reversed in this case it will be on some technicality; it won't be for lack of evidence.