Look for a large snare or barb wire trap, but be carefull. Looks like barb wire marks on the neck to shoulder area.
Certainly, if you see the deer afield, put it out of its misery.
Poachers in my area are reportedly using a crossbow. I have found their tracks (boots) on one of my trails on my property.
Bet that wound on the neck is arrow related.
The Hermit