Further re the Scottish Sun Editor's account, I can't see how he could have seen if the main rotor was turning or (virtually) stationary from "a few hundred yards away" at night. Unless, perhaps, the a/c had previously been much closer to him than that, which seems unlikely. However, if the AAIB are in luck, he may also be able to report any horizontal movement of the a/c as it descended.
Those of us non-helicopter pilots who are merely accustomed to helicopters overflying our back yards at about 500 ft or so - sometimes in transit, sometimes at low speed for survey purposes, and occasionally in the hover near railways or road junctions - have probably never witnesssed an autorotation training exercise. Don't think I have. Therefore, I'm wondering if I would describe an autorotation in similar terms to his account, i.e., "it fell like a stone." .
Assuming there was little or no forward airspeed, I have a question for you helicopter pilots. Starting from 500ft, and in the extreme case of no initial airspeed, what sort of stabilised ROD would be likely, and would it be normal to trade part of the height initially for some airspeed?
'scuse my ignorance...