The Associated Press just stated that the official position now is that the jet was hijacked. There are too many variables that are simply impossible in the event of a catastrophe. They now know that the transponder was turned off 12 minutes before the planes message system quit transmitting, which is impossible in the event of a crash. They're also now saying that it appears the jet was flown in a way to avoid military and civilian radar, something only a skilled pilot that knew the area could do.
So either the passengers and crew are on the ground someplace for some as of yet unknown reason and being held against their will, or one of the pilots decided to commit suicide and wanted to take everybody on the jet with him. It's going to be interesting to see what happens over the next few days.
If they ever do figure out what happened, count on it meaning more restrictions on passengers and better background checks on crews.