Answer
See step by step for the solution
Work Step by Step
a) 2 innocent, 1 guilty. 2 innocent men are telling the truth, the guilty one might be lying
Smith states Cooper was a friend of Jones. Jones however states that he didn't know Cooper.
That means either Smith or Jones is lying.
Williams states he saw Cooper with Jones the day he was killed. Jones however states that he didn't know Cooper. That means either Jones or Smith is lying.
Since we know 2 people are telling the truth, Jones is the one lying. That means he is the murderer.
b) Using the same logic as in a, we can deduce that if anyone is lying it is Jones. So again, we can deduce he is the killer.