D paid for a 40 p chocolate bar at a corner shop with a 5 note.A who served D was working in the shop while she finished a psychology degree. She was doing dissertation on people's levels of honesty by giving him 9.60 in change. She want to see weather he would correct her and tell her that he had paid for the bar using a 5 note,not a 10 note. He therefore put the change in his wallet and walk out of shop. It was only when he checked his wallet again just outside the shop that he realized A's error. D decided to keep the excess change.
Has D committed the crime of theft?
There are three possible answer yes , no ,or we don't know. What do you think the answer is?