if it was the sad act of an individual who had the extensive knowledge and cunning to perpetrate this - surely that person would want the world to know that they were that clever/sick! They would have left some note, tweet, Facebook clue.
I don't think this one is a problem. Two reasons for a start:
1) To protect the dignity of the family (very important in those cultures)
2) To enable them to get the full life insurance payout
I feel they could not have the self-control to leave no clue at all - unless the authorities have that clue and want to keep it to themselves.
The "clues" are probably fairly obvious, but until you have proof you have nothing at all in legal terms.
I cling to the the perhaps naive view that there are not that many commercial pilots out there waiting to take out their aircraft and passengers - waiting only for suitable "inspiration".
If there is someone like that up-front who has decided that today is the day then basically we are pretty much stuffed. New tricks for finding the wreckage afterwards are not that much of a comfort.
That's why I think the search will never end.