I haven't read the hundred's of opinions both professional and amateur here but I have noticed a few comments re radar both primary and secondary. Allow me a minute to explain. Primary radar is a basic skin paint return and is subject to slant range error. So if an aircraft at 37,000ft overflies a primary radar head, the radar display will not show the return as overhead the radar head's location but will push the return to a point about 5 Nautical miles to one side. This is because primary radar is 2 dimensional. A secondary radar return is synthetically produced by one or more SSR receivers and via a Radar Data Processing computer, a SSR return is electronically produced on the radar display. Thus you could say that a Secondary radar return is in effect 3 dimensional. So if an aircraft was to overfly a co sited primary radar head along with one or more Secondary radar receivers, then as the aircraft flies overhead at 37,000ft a 4 to 5 mile discrepancy between the position of the primary return and secondary return will be apparent.
This is not relevant as to why or what has happened to the Malaysian 777 but is an observation made by a recently retired controller with over 40 years experience