60 Minutes Australia says they know what happened. Spoilers ahead.
As has been suspected by others (and myself, fwiw), the report says the captain popped the cabin pressure and killed/incapacitated all the passengers. Then, with a final dip of the left wing so he could see his hometown, he headed out into the Indian Ocean to die. I guess he did it when the FO was out of the cockpit? Or depressurized and died with everybody else? I haven’t watched this yet, but I don’t think it covers any significant new ground, except saying that the pilot flew a very precise course to avoid suspicion before turning off the transponder and disappearing.