The communications were cut off from the cockpit. Only the pilot, or pilots could do that. According to the experts the wing flaps from the wing debris that washed up on the African continent indicated that the plane engaged in controlled descent. Meaning that somebody was in control and knew what they were doing. A true terrorist would have done his duty and crashed the aircraft into something to cause more damage, thus the theory of suicide is an obvious conclusion based on the limited amount of evidence.
I watched a program where the author of this theory was being interviewed... When asked ‘Why would the pilot commit suicide?’ his response was that looking at crash evidence was his expertise, and that they should ask somebody who deals with mental health issues.
The plane made a controlled descent and the likely pilot during such a maneuver would be the pilot, or pilots flying the plane. Maybe it was a suicide pact... And the fact is that we will never really know.