Why would suicide pilot not nose dive into the ground? - not enough mystery to embarrass the airline and the Malaysian government. That would practically be an open and shut case. The world would forget about it after two weeks. The world won't forget about this in a long time. The Chinese certainly think the Malaysians are muppets now. The pilot had just come from a trial were a former premiere of Malaysia had just been found guilt of corruption, and he was very unhappy about it. <speculation>: I wouldn't be surprised to find out that the pilot was in some kind of dispute with his employers - although if so, they certainly won't be admitting it to the media.
Actually, Anwar Ibrahim was not a former premier, and he was convicted of sodomy, not corruption. http://www.reuters.com/article/2014/03/07/us-malaysia-anwar-idUSBREA260HM20140307 Although there is some supposition that this was a way of targeting him, because he was an opponent of corruption.
Given the pilot's apparent close interest in the court case, perhaps he was gay? <speculation> Maybe a threat of exposure might have been a suicide trigger?
On another topic, there has been speculation that the pilot may have deliberated lowered the cabin pressure to incapacitate passengers and crew. I'm wondering how far the cabin pressure could be lowered? Could it be lowered to the same as the outside atmosphere (say 35,000ft)? Or would that take some kind of rupture of the aircraft skin?