On being a thief

John's in trouble again. His spate of thieving, something he's always done and doesn't seem to think it's wrong, has taken a really bad turn. He stole £20 from me on Saturday morning. I noticed on Friday night he had a lot of sweets, and I'd also lost £10 then but put it down to it falling out of my pocket. On Saturday I knew I had £40 in my pocket, 2 x £20 notes. I got a phonecall, could I go and collect John from the next village, so I thought I'd stop in the shop at the same time. When I checked the cash, I was down a £20 note. John denied it of course, but when we got home he admitted it. For weeks I've threatened him with "If you want to act like a crook, I'll treat you like a crook" and promptly locked him in his room. I Put a new bolt on the door, so he can't get out, and I also turned off the electricity to his room so he has a light and that's it. He had no food Friday night, and then yesterday I gave him 2 plain bread rolls and a jug of water. He stayed in there all day and all night, although at one point I left the door unlocked and he went out and turned on his electric. I pointed out that he's being punished and it was off for a reason.
The thing that really did me in was his attitude.

"Do you regret what you've done?"
"No. Why should I?"
"Because it's wrong. Don't you understand that?"
"No. Oh, Whatever."

He's going to be grounded this week, and at the weekend if I haven't seen a noticeable difference, he will spend another 48 hours in solitary. I will break his spirit.