I'm coming to the conclusion that this was a tail rotor failure.
The resulting enquiry will probably suggest changes to the standard operating procedures. Police SOPs, I believe, are quite liberal even over built up areas. I can understand that for serious incidents anything goes. In the case of a transit or lesser events then defensive flying has to come into play. Its not like your PPL(H) flying or regular military flying. Sadly mechanical failures don't respect any of this. For our non helicopter pilot readers I would suggest that helicopters fly more by mechanical means than aerodynamic!! There's more to go wrong!
Pilot incapacitation trumps all of the above.
FAA QHI 3000 Hours Helicopters. 10000 Total.