As understand it, dogs are in many respects like any other property...so usual first steps apply, are there witnesses to the gift? anything in writing (probably not) any proof at all of the gift (ad in the local free paper, did the person offer the dog to anyone else? Secondly are there photos or witnesses to the state the dog was in when your friend got it? Any proof of how it got into that state? If there is, then your friend might well wish to take advice from the RSPCA herself. I don't think that the courts would be that concerned unless the dog is an extremely valuable pedigree animal and it sounds like the police are on the side of your friend. Its a good thing that the dog has been to the vet, presumably he or she would be able to report on the state of the animal when your friend first got him?...might be worth mentioning to the dogs old owner that the police would probably be interested in any threats, harassment or ensuing vandalism. This is only common sense stuff ans I am no legal expert, are there any legal eagles or (!) beagles online today??