There is no detail of deer species
The report states that he "sliced the deer's throat": Halal slaughter? The World Animal Protection UK (Never heard of them) statement links this to poaching, if it was an RTA casualty (there is no suggestion that he was involved in the RTA that injured it) then how is it a wildlife crime i.e. poaching?
I can only think that the guy was prosecuted because according to the report he took it away alive and killed it away from where it was found. If he had killed it on the spot would that still be an offence?