VfrPete,
The 3rd pair of eyes is essential during high workload police ops such as pursuits. The camera-operating observer is heads-in working the kit, the pilot is monitoring the task but (quite rightly) making flying the aircraft his/her priority, so you need the 3rd person to maintain overwatch/ run air-ground comms. The folk on the ground watching the downlinked pics can ONLY see what the heads-in observer lets them see; there's always a lot more going on than fits into the picture frame. Although you could possibly operate the camera remotely from the ground, visual cueing would be woefully slower and less effective than having a human (or police - nearly the same (sorry Volrider/HnH - cheap dig)) expert operator on board.
EC135 generally,
Our T1s (with sand-filter, aircon, 2B1 donks and permanently-unserviceable-for-over-9-months autopilot fitted) have ZFW of 1912kg. Cat A ops? forget 'em! C of G? We have to make sure that our 2 pilots who are over 100kg never fly together! I have once seen the aircraft loaded with 360kg in the main tank, for a task which involved a quick nip up to the Northern border and back. My congratulations to the Eurocopter sales team; the aircraft is certainly not what I'd have recommended for the job here!