Do you have any proof of what they tossed over the fence? Do you have a vet report that says what the dog was poisoned with? You could absolutely file a case in small claims court for your vet bills and punitive damages, but you need evidence. In order for criminal charges to stick, they would have to be able to prove the crime “beyond a reasonable doubt.” The standard of proof in a civil case is “by preponderance of the evidence” which just means “more likely than not.” So even if the cops didn’t have enough evidence to charge them, you could still win a civil case. Just make sure you have a vet report that says exactly what made the dog sick. Without that, you won’t win. You have to prove that you (or your dog) were injured, that the defendant did something wrong, and that the injury was caused by the defendant’s actions.