Originally Posted by rogueteens

I find that hard to believe, the pilot would have to remove the co-pilot (also did this plane have an engineer too in the cockpit?) and keep passengers at bay for hours. Other people would have had to realise that something was wrong as it flew silently for hours and I'm sure that although the doors to the cockpit are now reinforced, it would not last out against a sustained attempt at breaking in.
My guess is that the people on board were all incapacitated by an onboard fire or leak that released poisonous gasses (I think that happened once to a Greek plane?) also I admit that wouldn't explain why the automatic responders were all turned off - unless its possible the fire also took them out?