I first thought it was shot down. Then I thought the passengers stormed the flight deck. Perhaps both of these things occured. The only way to know for sure is to examine the FDR and CVR. Until then speculation on this unfortunate flight will continue. The only thing I am sure of though, is that someone somewhere knows exactly what happened.
I hope it will never happen again. God rest their souls.

What I'd like to know about this flight is why it flew west for an hour before turning back east, towards DC or wherever. If the point is to have an aircraft full of fuel, surely a two-hour trip to target makes no sense. If the point is to have the element of surprise, again a 2-hour trip makes no sense. That seems to me a more interesting subject of speculation than some of these conspiracy theories.