Basically in my story a cop is forced to testify in court against the defendant who is a member of a gang. The cop however, is also a part of the gang, working as a mole for them in the police. The cop didn't plan to be testifying against one of the members of a gang, in which he is a part of. It just worked out that way. The cop has to play along and testify though, cause if he refuses, or tells certain lies, than the other honest cops will know he is lying and has something to hide. So the defense lawyer has to cross-examine the mole cop on the stand. The lawyer knows that the cop is a mole, cause the defendant told him. But no one else knows. So the lawyer has to discredit the cop as a witness to help his client. Would he tell the court that the client told him that the cop was a mole working for the gang? The cop would of course refute this to defend himself, but would a lawyer do that in an attempt to create some sort of discrediting of the witness with reasonable doubt?