Hypothesis; A is telling the truth, then the other three are lies, then several sentences can be inferred respectively: 1. A is number 2. Number three. B is number 4. D yes, yes. The second sentence and the fourth sentence are contradictory, and the assumption is untenable.

Assuming that b is true, it is presumed to be: 1. A yes. 2. ding is. 3. number 3.b 4 Ding is. The first sentence and the fourth sentence are contradictory, and the assumption is untenable.

Assuming that c is true, the presumption is: 1. A yes. 2. Number three. B yes. 4. ding is. There are contradictions, and the assumption is not valid.

Suppose ding is telling the truth. Presumption: 1. A yes. 2. Number three. Number b 4. No.

So the answer is; Ding told the truth. A is a criminal.