The second pair of pants
CJ pretends his dog bit him to excuse why he has the bite but he lies to his friend that he didn't even get a chance to put the pants on before he bit him. This means that the 2nd pair of pants which was logged into evidence and tampered with by the DA doesn't have a hole in them from where the witness's dog bit CJ during the murder.
SO unless CJ was murdering the prostitute with both his pant legs rolled up, the actual pants from the murder should have teethmarks/holes from where he was originally bitten.
This would have proved his set-up theory without needing any corroborating evidence.