The odd part is no distress call.
I’m no expert but I would have to believe that air traffic control noticed the plane descending. It went from 36000 feet to just under 6000 feet over a period of 10 minutes! Yet there was no communication between the cockpit and air traffic control?
Either the pilots were unconscious or else they intentionally refused to communicate with air traffic control.
If they were playing cockpit Boeing Boeing with the stews — they may not have been in any distress at all.