Tandem - a lot of people seem to opine on here that twin pilots fly along scratching their ass daydreaming about their next holiday...
IMHO that is certainly not the case for UK HEMS pilots, and I would be certain the same applies for police pilots, (I spent the best part of 10 years flying & instructing on singles before flying twins) as on task we tend to be very focused and constantly updating the mental picture, i.e. weather, obstacles, ETA, ETE, fuel, hospitals, IFR diversions etc.
I often fly in remote rural areas where we can be out of radio contact with both ATC & AMB CTRL for significant periods, so we very much rely on each other as a crew, and to give the paramedics credit, the most experienced ones are extremely capable navigators as they know the patch intimately (sometimes down to individual buildings) and will also be thinking about fuel, obstacles, ETA etc. when not talking/thinking medical. Anything unusual, e.g. vibes, cautions, warnings, gongs, strange noises etc. will be spotted and announced pretty sharpish by the front seat TCM in my experience.
As for:
Finally, where do the witness statements of 'fireworks' or 'sparks' fit into this scenario?
That I would like to know too, and I would not discount the witness statements out of hand.