Opossums usually don't come out during the day and hawks usually try to haul their prey off. I'm thinking based on your description it's a mink. Nasty little things....pretty much kill just for fun. A game camera could help you determine the issue but simply a live trap or two would be most helpful. Mink and foxes are very smart so whatever bait you use be sure that they can't run off with it. I had a fox last year I was trying to catch. He wanted the bait so badly but not enough to get in the trap. He dragged the entire trap over trying to get that fried chicken .Well, we live on a wooded ravine, so just about every predator you can imagine. We have a 5' fence around much of the property. About 6 mons. after we lost our last lab in Feb 2022, started seeing a fox inside the fence, which was a first. The labs probably kept many predators out for years.
Sometimes the girls venture outside the fence to our surrounding woods. We have lost one outside the fence, which is understandable. But since last September, we have an issue within the fence. We have lost 2 within the last couple of months to violent attacks. Attack at the neck ares and side slashed open, with abdomen eaten. One additional attack left only the head, wings, and legs behind (minimal feathers around). Figured this one was a ferel cat. Assuming the other 2 were either a hawk or oppossum. All happen in the day.
We have always free ranged, and for a year had no problems. The coop and run are predator proof with 1/4" hardware cloth on all sides and base of the entire coop/run. Roof over the coop and run. So the probelm is not in the hen house.
Unfortunately,, we are on someone's radar...
Another thing you could do is get a roo (if allowed) to protect them. I agree the dogs more than likely kept your predators away. You could also make staying in the fence more appealing with treats. One of my girls only ventures outside the fence to eat the neighbors bird seed.