Son of the Mob book - what was on the tape that was erased?

When Vince asks Ray who responsible for the Calabrese hit, Ray produces an audio cassette tape. Vince recognizes the voices on the tape, and he realizes that it was his mother who arranged the murder. His father knows nothing about it. His mother was not taken to trial, however, because a young Kendra had used that cassette to record her karaoke. Her singing covered the evidence so it wouldn't hold up in court.