[Don Plumley]

Since conjecture is free, here's my scenario.

Pilot mad at government, wants to fly the plane into the Petronas towers or other landmark to make a point. After co-Pilot makes the hand off from Malay control, he steps out to take a leak. When he comes back, he notices the flipped breakers before the pilot is able to incapacitate him. A struggle ensues. Pilot kills/disables the co-pilot, depressurizes the plane and kills everyone else. But he is wounded in this process/does not mask correctly/etc. and the plane flies on the last designated course until it runs out of fuel.

I'm unconvinced that a bad cascade of mechanical problems prevented any communication. The sequence of turning off the breakers to me means something nefarious was in play.