Another big twist to the 2G spectrum scam case has emerged. The CBI has discovered a shocking breach of rules. An audio tape has emerged revealing CBI's senior public prosecutor A K Singh tutoring Unitech M D Sanjay Chandra, a key accused in the case on how to counter prosecution charges. Even as Sanjay Chandra has described the tapes as concocted CBI has replaced Singh and sought for a probe into the episode.