The following is my theory as to what really happened.
Before MH370 took off from Kuala L., it was secretly loaded with lithium batteries which were only supposed to be allowed on cargo planes because they are combustible. As the plane was accelerating down the runway, an underinflated front tire began to catch fire which went unnoticed and when the the plane left the ground , the tire was retracted into the body of the plane just under the cockpit.
After it took off, the fire spread to the cockpit which was over the the burning tire and then spread to the batteries in the cargo bay behind the cockpit.
The pilot reported the fire to ground control as he began losing control of the plane. Someone on the ground realized what the REAL cause of the fire getting so large was (lithium batteries) and then instructed the pilot to head out to sea and to try to land the plane on the water. Malaysia ground control sent 2 jets after the plane with instructions to shoot it down ONLY if it appeared to be veering towards land.
The fire caused the plane to crash into the ocean. The jets notified authorities of the crash site.
Salvage ships soon arrived at the crash site and collected debris. Whatever was too large to be salvaged was sunk.
Subsequently, collected crash debris that showed no signs of smoke damage were scattered here and there to confuse investigators as to the real location and cause of the MH370 crash.