view of retired 747 pilot on mh 370, page-10

"How does your 747 dude explain the fact that the transponders were turned off a few minutes before the last radio call?"

This is why I think it's suicide. The transponder was turned off, then the plane fly in the completely opposite direction to where it was actually supposed to be going. If you didn't want the plane to be found this is exactly what you'd do. They will probably never find this thing as once the black box transponders run out of gas they'll never find the thing. I cannot think of a reason why the plane turned around 180 degrees and flew on for a few thousand k's.
The other suicide I remember (from Air Crash Investigations!) was a freight flight in the US I think were the pilot tried to kill his co-pilot and engineer with a hammer I think. He was eventually overpowered but it's possible something similar happened.