the indication from the learned aviation expert/ex regulator on the Beeb this morning was that the plane had descended in an orderly rapid fashion, that they hadn't engaged in a reroute to look for landing or put out a mayday, the sequence being in that order....this could have been indicative of a cabin depressurisation, the question being for the passengers if it had been severe, then it would have been unconsciousness pretty quickly......
So what caused it? Speculation about a small bomb may well emerge - the plane had also been checked over the day before, a small repair to the landing gear effected but that wouldn't have led to a depressurisation incident though.