(1) Assuming that B is telling the truth, then D is a treasure thief, then: ①C is telling a lie, and the treasure thief is D, not B; ② What D said is also a lie. They have no enmity, that is, they have not wronged him. He is a treasure thief. What 3 A said is a lie, then A may also be a treasure thief at the scene, and then D is a treasure thief, which is not true; So this assumption doesn't hold water.

(2) Assuming that D is telling the truth, then: ①B is telling a lie, D is not a treasure thief, ② C is telling a lie, then B is not a treasure thief, ③A is telling a lie, then A is at the scene, committing a crime; Therefore, A is a treasure thief;

Answer: According to the above reasoning, D is telling the truth and A is a treasure thief.