From what I know of the case of poor PC Harper. He was dragged for a mile or so after his legs were caught in straps trailing from the quad bike. Now I'm guessing the main crux of the case being a murder or manslaughter charge, hedged on if they were aware they were dragging a 6ft copper along or not, and if they did was it intentional? Obviously a clever barrister managed to convince the jury they had no idea, despite leaving the scene of carnage. I'd also wager heavily there were attempts to either intimidate or noble the jury.
I'm sure the judge was not happy with this ruling, and an appeal is launched to overturn the conviction, and we see a murder verdict.
I'm hoping this is the case, but British justice is often roulette.