Your story has been in my mind since I read it and saw the pictures. I'm so very sorry for your trauma, but feel this was definitely done by humans. Surely any animal predator would kill to eat and they certainly wouldn't line them up after dispatching them! I would feel very unsettled if it were me and would report it to the police. It's not "just four dead chickens" . It's trespassing on your land, causing deliberate pain and cruelty to living creatures and destruction to your property. I would feel very vulnerable that whomsoever did it would return to do more damage so the police really do need to be involved. Tell your neighbours what happened (I'm sure you've done that already) and maybe put it in the local paper. What's occurred here is by no means trivial, but a sinister act of cruelty and wanton violence and whoever did it needs to know they can't get away with it. Next time they may attack a child or elderly person. I apologise if I seem to be OTT, but this sort of thing really bothers me and shouldn't be ignored. I do hope you keep us informed of any outcome, but in the meantime, I'm sending you my best wishes and kind regards.