As far as I have been informed, the loading was actually secured correctly, but due to the pilots fast(-er than usual) ascend to avoid becoming a target for terrorists, the 5 MRATs on board have been able to break lose from the securing (as it was not meant to withhold these G-forces), and moved through the plane. Which resulted in the tumbling which is clearly seen in the video, and this tumbling actually sent the aircraft in a stall, from which it couldn't recover. The result we all know...
R.I.P to the 7 people on board.
cheers,
Jona L.