Either you believe the plane crash on the spot where the radar lost the plane or the
plane continue to fly with the transponder OFF.
If you believe the plane crash, where are the debris ? So far, everyone manage to find some garbage from ships but no debris from the plane.
If you believe the plane continue to fly, where does it go ?
The military radar pick up an unidentified aircraft from the spot where MH370 went missing and trace to Straits of Malacca.
Therefore, my theory is that the plane encountered some problem, may be an electrical short circuit and some of the equipment like radio, transponder and auto pilot are not working.
The pilot decide to make an emergency landing.
He have 2 choices
1) Continue to fly straight to land in Vietnam in the dark to find a run way, which he is unfamiliar and no confident he can find the run way without help from Vietnam control tower.
2) Turn back to KL airport, where he have perform landings many times.
I believe he turn back to KL. However, he need to fly manually in the dark so the plane went off course and overshoot to Strait of Malacca. At this point, other equipments also start to fail so he have no choice but crash land at Indonesia.
I don't think the plane crash into the sea because there are many ships that pass through the strait without noticing any debris. The most likely place to crash is the Mangrove swamp because the mud and vegetation would cover the plane and make it difficult for someone to see it. There are no explosion because of the soft mud and as a result, nobody notice the plane in the swamp.
That is my theory.