We are going on one leaked report that banging was heard on the door.
That one of the pilots could not gain access.
If that was true and there is NO official statement to back that up then if the other pilot could not gain access it would mean that the other pilot had locked the door.
If that was the case then I cannot see any possible explanation of pilot incapacitation as it would have taken a conscious decision to lock the other pilot out and the conclusion can only be with bad intentions.
But we are relying on a leaked report which has hit all the tabloid press today.
I am not an A320 Pilot but a corporate jet pilot and we do not have doors to the PAX but lets take another innocent scenario that the door was not locked from the inside?
Reaching a high level like FL380 will make two things more likely firstly a depressurisation and secondly once the climb phase is complete and the aircraft is established in the cruise is the most likely time that a crew member will leave the other crew member at the controls and go back to the toilets.
Even with the banging on the doors IF that is correct and failure for the other pilot to gain access it does not preclude the possibility of depressurisation with one crew member at the controls and the other in the toilet.
The other pilot in the toilet would realise something was seriously wrong and attempt to join his colleague but within seconds would be becoming muddled and probably unable to put in the right code or infact entering the wrong codes in desperation he would hammer on the door before loosing conscious while having a door which is normally functioning
I still find it hard to believe its likely that a crew member (not impossible) would take himself out and 150 PAX on purpose and a more obvious reason even given the door banging could exist
There is no evidence that the door was locked from the inside