A possom will kill one or two anytime it's hungry. They eat the intestines of the chicken. I don't know if the chicken is killed before this eating starts or not since I've never caught one in the act. No matter, possoms are predators and carry desease and will do you no good at all. Do not allow them to remain.
The layers I've had kill by possum went in through the rear end. The chicken look untouched other than it rear end eaten out. No blood anywhere. My dog just has a nose for a possum and find one about every 4 days on average. Early in the morning up a tree, in the day time in a hollow log, he finds um and I shoot um. Sometime I just let him do his thing and he kills it, but in a tree I shoot it our. I've killed quite a few this summer. The possum is the only predator I've had any problem with. The dog seems to keep everything else away.
Possums are by far the most frequent killer we have. They were reaching through chain-link fencing and pulling the heads through, and eating most of the head off. Because we had some dogs and cats we didn't want injured, we put out these traps;
We have caught many coons and possums with these traps. We did install 1/2 inch hardware cloth along the fencing and, it worked. I keep the DP traps baited and continue to catch possums. The coons seem to have caught on and stay several hundred yards away and rarely ever approach my yard area. Possums are kinda like me. They are almost as stupid as they look!