So sorry to hear this. It does sound like dogs. A few years back I'd turned my small flock out to graze around the barns. I was in and out and suddenly saw dogs out there. They had partially ripped the throat out of a 100+# wether. I had to finish him off. I had gone for a gun but the dogs were gone by the time I got back. I strongly feel like they were hunting dogs (either pig or coon) who'd not been picked up after a night hunt and were heading home. I did not ever see them again. I did a few years later see some hounds cutting through my bottom pasture which I headed off before they discovered the sheep. I did get a GP after the first incidence but that had it's own problems, mainly containment. You pretty much can't keep one in if they are determined to be out. We are to near a highway for my comfort to have one out patrolling on his own. This GP was more of the patrol variety than the hang with the sheep type. I've since improved my fencing to make it less easy for passing dogs to just wander in. When I have lambs I don't ever let them out of the best fenced pen until they are well grown.
I know I can't predict when dogs like that might pass by. There is no telling where they came from or where they were going.
Wild animals are bad but domestic dogs on their own can do way more damage. Wild animals only take what they need.