Return to the question of "tumbling"
If the rotor was stopped, then there's no gyroscopic stabilization, and it would be possible for the aircraft to have been "tumbling" as witnesses suggested.
While eyewitnesses are not necessarily able to assess or report the true motion in 3D, the helicopter "tumbling" is not ruled out as it would be by the presence of angular momentum with the rotors turning.
Turning at 20 radians/s the 200kg 10-m-diameter rotor has an angular momentum of order 100,000 kg m^2 s^-1, requiring a huge torque of order a million Newton-metres to make it turn end-over-end at a radian per second.
With the rotor stopped, the whole helicopter has a moment of inertia of only a few 1000 kg m^2, turning quickly in any axis when a torque of only ~10,000 Newton-meters was applied.