Did someone take over Flight 370?

There is still much that is mysterious about the fate of Malaysia Air Flight 370, but there is emerging consensus that the passenger jet bound for Beijing changed course, flying west over the Indian Ocean and flew for at least four hours. This tends to suggest that there was a human intervention, rather than a mechanical failure.
Typically such a human intervention would be a hijacking for political purposes, as was the case with the 9/11 flights or any number of other hijackings.
But no credible terrorist group has asserted responsibility for this operation and whoever diverted Malaysia Air Flight 370 issued no demands, which would be typical in the case of most hijackings.
There is always the possibility of pilot suicide, as was the case with EgyptAir 990, which plunged into the Atlantic shortly after leaving JFK Airport on October 31, 1999. The National Transportation Safety Board determined that the co-pilot intentionally caused the crash, although Egyptian authorities questioned that judgment.

But if Malaysia Air Flight 370 was a case of pilot suicide, why fly for so many hours and go through the trouble of switching off the transponder?
This leaves open the possibility that a person or persons with non-political or idiosyncratic motives commandeered the plane.
This is more common that one might presume. In the pre-9/11 era, before the introduction of reinforced cockpit doors, there were quite a number of such cases.                                       Read news in full 14/03/14 Peter Bergen/CNN