Our 6 year old son has had issues since learning to walk. Defiance is key with him. He has ALWAYS done whatever he wanted, whenever he wanted. As I’ve said above, we’ve done everything we know how, and everything counselors have told us to do and none of it works. The scariest thing is through all the consequences, through all the rewards, through all the extra attention and ‘time-in’, he just doesn’t care. He will look you straight in the eye and say “I stole, I know it is wrong” with no remorse, no care. You can cry and be honest with him how it saddens you as a parent and he looks at you blankly.
First off, I'd recommend two powerful books: The Explosive Child by Dr. Ross Greene, and Beyond Consequences, Logic, and Control, by Post and Forbes. Perhaps these authors will make some suggestions that you have not yet tried.
Since you say he doesn't have access to empathy, which is a higher brain function that is based upon having a regulated nervous system, then it makes sense that guilt and crying and all that other stuff that may seem to work with your other kids won't penetrate his shell. It sounds like he may be closed off due to some kind of internal distress.
I'd wonder if he experienced some kind of separation or trauma at a young age. If so, there are therapies that can repair and restore whatever was disrupted in his development. Dr. Bruce Perry's work is well regarded on this subject. I'm not sure how you found me, but if you are in the Boulder area, I can suggest some therapists who have excellent reputations for unwinding trauma responses that impair normal functioning.
I'd also want to make sure you have had him professionally evaluated, perhaps by a psychiatrist or neurologist. He could have physical or cognitive issues that are in his way.
At the risk of saying something you already know - if consequences aren't working, it may be time to focus instead on figuring out what he is attempting to achieve with his behavior. For some kids, wanting something they don't have is almost physically painful. Couple that with immature strategies for acquisition (I'll just steal it), and it's double trouble. He may benefit from very specific guidance while learning and implementing more socially acceptable ways to get what he wants. He may also need a lot of help managing the intensity of his own feelings.
Sometimes, consequences alone don't work to prohibit behavior because they teach a child what not to do, but don't teach another way to meet their goals. Not all kids are wired for successful obedience or imitation. He may need you to break things down into baby steps and give more explanation than is necessary for your other kids.
Sometimes, parentally applied consequences intended to change behavior actually make the behavior worse. The cycle looks like this: the child feels bad because he really really wants something and doesn't have it. His desire makes him unable to think clearly, so he just takes it. He feels better momentarily. Then he gets in trouble -- consequence, punishment, someone gets mad at him, or whatever. He then feels bad because he really wants love and approval and doesn't have it. His inability to think clearly while in distress gets him in more trouble. You can see how this leads to perpetual stress for everyone involved!
What might break this cycle is a loving and empathetic intervention when he feels bad about wanting something he doesn't have. We can talk some more about how that might sound in a session if you'd like.
I hope this helps. I commend you for your dedication and motivation in continuing to search for something that will work. You are surely a blessing to your family, and I hope you can find some time to nurture yourself in the midst of this very challenging situation.