Ya know, I don’t immediately jump at the idea that it was the younger co-pilot. Guy seems to have had his stuff together being a co-pilot on a 777 at 27 years old and all. Could be, but, maybe the pilot went off and did something crazy here.
Don’t know yet. May never know.
I think the plan required a pilot in the cockpit and a hijack team in the cabin. One or both pilots.
If there was somebody else in the passenger list capable of flying a 777 and switching off the commo, that can be discovered fairly easily.
The pilot was the one with the simulator. He could have ‘flown’ just about any scenario he wanted. Practice, practice, practice...