The primary opposition leader in Malaysia was sentenced to 5 years in prison just seven hours prior to take-off of the flight. Ahmad, one of the pilots, was a big supporter of the opposition leader and was even at the trial when the verdict was handed down. It was noted that Ahmad was "clearly" upset over the verdict prior to climbing into the cockpit. My conspiracy theory is that he and the other pilot got into an argument over the sentencing, the 'opposition' pilot killed the other one during the argument and then it was "Look what I've done, what can I do now?...I'll just fly this bird until it falls out of the sky." Knowing the Gulf of Thailand was only a couple of hundred feet deep he turned the airplane around toward the Indian Ocean where depths easily exceed 10,000 feet and where the plane could be lost forever.
...or aliens abducted it. :-D
Whatever the case, today the plane is attempting to settle a littler deeper into the sand beneath the weight of thousands of feet of salty water...possibly never to be found.