There have been many statements that the two pilots did not ask to be on the same flight.
There have also been musing as to why the aircraft turned back to the west if the intention was to go west why not take an aircraft that we routed to the west.
Is it possible that the two pilots took the opportunity presented when chance scheduled them on the same flight? That the flight was scheduled for the wrong direction would account for the turn back.
Against this is the appearance of evasive routing to avoid or confuse detection.
So, had the two pilots flown together before? Had they flown this sector before? When were they scheduled for this flight?
We know the Captain was probably fatigued following his activities before the flight; what about the FO? Was he properly rested and might he have been the PIC?
This appears to suggest one or other pilot was to blame but I don't think these questions have been posed or answered, especially given that initial positive statement that they didn't ask to fly that sector.