We could learn quite a bit, for instance, if the voices on the recorder were neither of the flight crew, or whatever the subject of what was said could suggest

We could learn quite a bit, for instance, if the voices on the recorder were neither of the flight crew, or whatever the subject of what was said could suggest whatever had happened at the diversion ... unless whoever was smart enough to disable the transponders would disable the cabin mic, which would probably be the least informative condition