I've been thinking about your situation, and as much as I'd like to see justice done to these people, I'm not sure immediately running to the police is the best idea.
First of all, if they treat animals that way, it's not a far jump to humans.
Secondly, if it's blatantly obvious that you were the one to call the police, or if they were somehow able to discover it through magic, then depending on their relationship with you, it may be extremely likely they would attack you either physically or magically. And if you'd have to testify at a trial, they'll know for sure.
If you have any lawyer friends, or can get in touch with any law teachers or advanced law students, you may want to ask them how much of the activity is illegal in your state, and what kind of evidence would be needed for a search warrant and eventual conviction.
You could also call the SPA, although if they paid a visit it might get as bad as if it were the cops. There would be less tension, and the SPA probably wouldn't be able to enter without the police, but again it might be glaringly obvious it was you.
Seriously though, unless you want to try to force them to stop and raise hell in the process, I wouldn't do anything drastic until just before getting out of the whole situation for good.
And if all you are truly concerned about is your own safety, make a break for it as soon as you can...