An inhabitant has been killed in Knavesville and the Sheriff has interrogated four suspects. It is known that one of them is the killer. As is expected of Knaves, they alternated between telling the truth and lying (Not necessarily in that order).

Each suspect was first asked if he was the killer, to which the sheriff got the same answer from all the four suspects.

He then asked them, 'Who was the killer?' The answers to which are shown below.

Abbey said: Bart is the killer.

Bart said: Dean is the killer.

Cody said: Bart is lying when he says Dean is the killer.

Dean said: If Abbey did not kill him, then Bart did.

Who was the killer?

B and C contradict each other, so one must be lying and the other must be telling the truth. In the first round of questions, it must have been the other way round, so in any case one of them is the killer.

If A answered the first question "Yes" (lying) then B is the killer. (B answered "Yes" telling the truth, C lied, and D lied.)

If A answered the first question "No" (telling the truth) then C is the killer. (B answered "No" telling the truth, C lied, and D told the truth.)