So, if there aren't any fingerprints that match those of the clerk who rang up the sale, defense could claim the tarp cover blew out of the back of the garbage truck as it was making it rounds, etc.
If indeed this tarp cover was the wrapper of the tarp purchased along with the shovel, hat and gloves, it will have the fingerprints of the clerk on it unless whomever handled it after the purchase wiped all the fingerprints off.
For all we know, the person who made the purchase at Walmart was wearing a disguise or their face cannot be seen.
Let's all hope there are fingerprints on that wrapper that will bust Doug. There is no way he would be able to explain why a tarp wrapper with his fingerprints on it ended up near the abduction site while claiming he was 14 hours away in Virginia!