Serious but graphic question about a dog I found...severe animal abuse...kinda long story?

No one will laugh at you for reporting a possible animal abuse case. There may not be anything they can do if the animal is no longer available for inspection but it's worth it to at least try. If not, there's no way that the person who did it will face any charges. At least by calling you're giving the animal some respect and trying to help other dogs that may be harmed by this person in the future.