You are using “western” logic. Remember, the captain was Malay, and “loss of face” is devastating. All of the machinations of the company and government have been dictated by this philosophy. Does Air Malaysia keep a handgun in the cabin like some U.S. carriers do now? Pilot 86s the co-pilot, heads up to fl460 which takes care of the passengers and rest of crew, sets the auto-pilot for the Roaring 40s, takes off his mask and goes to sleep. Hard to prove suicide at those depths.
It is or it isn't, and no court of law will save him if it is. If their deity is all-knowing, it doesn't matter what humans think. Even in Islam, their god will know.
Let’s see if they find any floating debris on the surface, find or at least hear the CVR and/or FDR, and see if sonar detects the wreckage at the bottom of 23,000 feet of water.