From post 598: "My feelings too. No visible damage to the MRBs does not necessarily mean they weren't turning, just that they weren't turning under power, or they never struck anything."
The image in the link below (it is the penultimate image in the slideshow) is one I have frequently retuned to. Given that much of the roof area has been discussed in this thread, I am surprised (as far as I can see) that what appears to be obvious signs of some (albeit minimal) signs of MRB movement has not been mentioned.
The visible damage to the roof, by what appears to be rotors running counter clockwise, would seem to lend some interpretation of the velocity of the aircraft, the speed the rotors were turning, and perhaps even the pitch of the rotor blades.
BBC News - In pictures: Helicopter wreckage lifted from Glasgow bar
Of course all we purport here is conjecture - some of which is more informed and informative than others; with this in mind, on discussing the suggestions offered in this forum with my husband he raised the hypothesis that perhaps an incident in the cockpit (such as a damaged CS canister) could have been in some way responsible.