From the CCTV vision, at or shortly after TDP, the helicopter dipped nose down and spun to the right, and entered into a high rate of descent. It's clear what the helicopter did, but there could be a few causes, like main or tail rotor control malfunction/hardover, physical failure of the tail rotor or drive, MGB failure, engine(s) failed resulting in a MR overpitch and loss of control, pilot incapacitation and consequent control loss due excessive inputs or (least likely) deliberate inputs from the pilot to crash. Crew responses to all these possibilities are different - suffice to say that when this machine malfunctioned there was no hope of recovery or steering in any direction as it descended at a very high rate to the ground. Appears the TR stayed with the helicopter until impact - unlikely it "fell off", even though the response of the machine is identical to what would happen if the the tail fell off.
Root cause is unknown - made worse by the fact that this is a near-new modern helicopter - and this will be watched carefully by all operators of Leonardo products world wide. This will be a much anticipated investigation, and one I sincerely hope is conclusive. Vale Khun Vichai and all POB.