The only thought more appalling than the fact of this tragedy, is the terrible thought that we may never know what happened.
If, as seems to be accepted, someone deliberately turned off all comms and flew the a/c seven hours away from the original flight path, then it's a reasonable conclusion that they do not want it to be found.
I assume all circuits in a modern aircraft have circuit breakers. This presumably includes the CVR/CDR. It would seem logical to hit that breaker as well. That would be the ultimate insult to the victims, assuming the airframe is ever found.