A thought about the locked door, and the entry code.
Everyone assumes that the pilot outside could enter the correct code, and therefore the copilot had to have been entering over-rides. Therefore was conscious, and all that implies.
But, there's a very simple electronic fault that could change that scenario radically. Suppose one of the code entry keypad buttons went flaky?
I doubt there's a display showing the code numbers as they are entered. So, a faulty button in the keypad would result in the pilot entering his code, the code failing, and possibly he doesn't even know why.
I wonder if the code entry pad even makes a beep or something as the keys are pressed? Even if so, there are some keypad circuits that use resistor dividers so that each key produces a distinct output voltage, then a micro works out which button was pressed by doing an AtoD. If it was that kind of keypad, a component fault or even a bit of conductive dirt could give wrong numeric button values, while seeming to work/beep, etc.
What's the bet the cockpit door security keypad wasn't designed to the same failsafe standards as the flight instrumentation?
If what happened was something like copilot has brain aneurysm, then pilot can't get back into cockpit due to faulty keypad button, that would have to be a record for the cheapest part failure causing the worst accident.