I'm truly sorry for what happened. I would have been a basket case if it happened to me.
I know ferrets like the back of my hand. I was seriously involved in the American Ferret Association (AFA). I bred them and also would take in unwanted ones. I was a senior judge at ferret shows but it wasn't just a show. It was one of the best ways to give out information. People needed to know if a ferret was truly the right pet for them.
Believe it or not, most of the ferrets I came in contact with were well behaved except for some of the give ups where most people got them on whims and treated them as throw away pets. I knew how to handle more aggressive ones because I was experienced but they became permanent residents. There was no way I could adopt them out with those temperaments.
In the 90's, we, in Maryland, got the state legislature to officially declare ferrets as domesticated and we're added in the same category with dogs and cats. That includes the laws associated with it such as a rabies shot being required. If it's a law in your state I doubt those people would have had it done. Then they could be reported for that too. It's not much but it's something.
The law was also changed on the minimum age ferrets needed to be to be sold so most pet stores stopped selling them. With this we hoped it would cut down on whims and a
anyone who really wanted a ferret would look us or another organization up. We never made money off selling ferrets. In fact it cost more keeping them. We mostly wanted to make as sure as possible that they were going to a good home with people that had a very good idea of what having a pet ferret would entail and realize they were very social and needed time out of their cage and enjoy playing with their human family. The one thing to know is that they have very tough skin so are used to biting down hard when playing with other ferrets. You may need to teach some of them to be more gentle so you scruff them by the neck and tunk them on the nose.
I've worked and had many types of animals and I've loved each and every one of them but ferret people have to face the facts. Ferrets have been known to kill other animals. In fact it pains me to say that one time one pof my ferrets got into my cockatiel's cage because I was careless. One thing to learn about ferrets is if they can get their head through an opening, they can get their whole body through. That's how Willow got out of her cage. She dragged Oliver out of his own cage while I wasn't home and killed him althougph she never tried to eat him. He was like a toy to her. I had to call a friend to look for him since Willow dragged him somewhere else. I didn't want to be the one to find him. I was so upset. Even talking about it now brings back some of the pain and that was almost 20 years ago. I hated Willow for what she did but I had to remind myself that she wasn't human so it wasn't malicious. The fault was mine, just like those people that owned the ferret that killed your chickens.
Those people should definitely pay for your losses but I know that that's not what was and is foremost in your mind. It angers me how people could care less of how what they do or don't do could effect others. The world revolves around them. Then they say that they're only animals. They can be replaced. (Yes. I've run into people like that.) I wish there was some way to really make them pay and I don't mean with money. Then maybe they would think twice about doing something like this again.