There has been much talk of the Malaysian military primary radar and actions consistent with a deliberate act but I haven't seen a trace or any justification for the consistency statement. Do they mean it flew straight and level, or that it performed nice rate one turns, or an impressive aerobatic sequence? I am suspicious at the apparent confusion from the Malaysians.
If the Vietnamese were looking for it after it failed to make contact, isn't it inconceivable that the Malaysians weren't doing the same? If they were, and the military were tracking it and it was flying in a controlled manner, what would be their next actions. Intercept? Shoot it down if it was heading for land and not responding? If that had happened could they obfuscate the investigation to avoid detection of their action? Which governments would be complicit in such a cover up?
No one wants the spectre of a successful hijack to reenter the geopolitical domain.