There are pictures of his hands. They are not the manicured hands of a law clerk. He may or may not have been wearing gloves when he removes the battery and the plates. It's not even certain that those things occurred at the same time. Regardless, I don't know what his hands have to do with his level of intelligence, so I'm not sure what you're blathering about with a lot of this post.
I do think he's dumb but not so dumb that he was incapable of doing some level of trying to cover his tracks, like by cleaning up a large bloodstain in his garage and possibly shampooing his carpets. It doesn't take Dexter to do those things. I don't think Dexter would have left his blood in her car, his DNA in her car, her bones in his firepit and burn barrels, her belongings in another burn barrel, her car key in his bedroom with his DNA on it, and a bullet with her DNA fired from his gun in his garage. Otherwise, great analogy.