The mystery of flight 370

For those of you who don't remember the different conspiracy theories regarding the 9/11 attack, let me refresh your memory. The picture of the plane that struck the second tower looked like the plane was a military plane at least from the underside from the picture. It was said at the time of the discussions that it was possible to fly the passenger planes from afar by remote control or take over the planes control from those flying the plane. Of course if that was possible then it would also be possible to shut down communications and the transponder. This brings us to the latest in conspiracy theories about the total disappearance of the Malaysian airliner Boeing  777 flight 370. 
Let's look at a few possibilities ...
1. The plane had a catastrophic failure that was instantaneous, resulting in the total and utter destruction of the airframe and cargo and passengers over the last known position of the plane. But no wreckage found in that area. This possibility now under scrutiny because the engines were sending back data that showed the planes engines sending data for four more hours. 
2. The plane was flown off course by error until it ran out of fuel and crashed into the water far away from the original last posted location or flight path. Seems like there would be a call for help from the flight crew and the transponder would still be working. 
3. The plane was hijacked by the flight crew or others on board and terminated the signals from transponder (one switch turns off the signal) and is flown to land in a unknown location. 
4. The planes controls are taken over by remote control and all communication and telemetry from the plane is turned off. The crew and passengers are held hostage in flight and cannot terminate the remote control of the plane. The plane is flown to a unknown location. 
In case 3 above the passengers may not know the plane is off course until the plane touches down. The passengers are then deplaned and terminated.
In case 3 & 4 above the passengers could be gassed and terminated in flight or upon landing. This would explain the phones being called and no answer, although a ringing phone is no indication of the phone receiving a call. 
Both 3&4 above suppose the plane is taken for another purpose other than holding any for hostage or any "normal" hijack activity such as money, release of dissidents or asylum. As of yet no one has asked for ransom for the passengers. 
This of course leaves the question ... If the plane was hijacked what was the reason and for what would it be used???