Man sorry to hear that. It's bad regardless of what happened or who did it. Nothing deserves to suffer like that. I'm not a cat fan but I am an animal lover.
We had suspected a man doing the same to my old Black Lab but could never prove it. We just figured since he hated everything he must be eat up with something evil and he lives in his own hell. Ben stayed in our yard but anything could be thrown over a fence. That being said, don't let your anger make a bad situation worse (like I wanted to do more than you know!) Because then you have pets that are gone and potential lawsuits, fines or jail time.
I'm feeling your pain and it really brings back some aweful memories. Keep your head up!