Tial by liars

[bonanova]

Alex was charged with robbing a bank. At trial Ian testified that Alex had committed more than a dozen robberies during his lifetime. Jamie denied Ian's statement. Davie then opined that while Alex may not have committed a dozen robberies, he had in fact committed at least one robbery. It was later determined that only one of the witnesses had told the truth. Was Alex guilty?

[Morningstar]

If I'm reading the problem correctly, Alex is being charged with a specific robbery. Even if he has committed robberies in the past, he's still innocent if he did not commit this one.

Ian's and Jamie's statements are inherently contradictory. I believe therefore that one of them must be true. If Ian's statement is true, and Alex has committed more than 12 robberies, then he has committed at least one, which makes Davie's statement true as well. Since only one of the statements can be true, both Davie and Ian are lying. Jamie is telling the truth, and Alex is innocent.

[dark_magician_92]

no, he isnt, if i am not wrong

[bonanova]

Both d_m and Ms got it right. I marked Ms's post, in order to point readers to the logic he provided.