Once the officers had assured each other that no one was having a bad trip, they did a closer inspection and found that what the dog was biting wasn't the ground at all, but the illegitimate love child of Chewbacca and Swamp Thing.
"Arrrrrrr-ghghghghgh!" (Hey, let's see you try to spell the sound Chewbacca makes.)
Actually, it was Liascos, wearing an outfit that would later earn him the nickname "Moss Man." Officially, it's called a ghillie suit -- the type of camouflage that snipers use to blend into the foliage when shooting from grassy knolls. He hadn't yet stolen anything at the moment he was caught, perhaps because he realized the grass suit wasn't a great means of disguising himself once he was inside a rock and mineral museum (dressing up as the Thing from The Fantastic Four would seem like a better choice).
Albeit not the subtle choice.
Of course Liascos denied the whole thing, claiming that he was just trying out a Halloween costume that his kids had given him. Then he promptly went on the lam and is still out there somewhere, presumably pretending to be someone's backyard.