I had a similar situation happen to me about 2 months ago, except it is my neighbors dog. We got animal control involved from the beginning (we had previous problems with his dog getting in our yard, and they met us at the vet clinic). It scared him enough that he now keeps his dog completely contained, and he paid the vet bill (it was about $200 without xrays, but the puppy did have puncture wounds). In all honesty, mistakes do happen. Hopefully he learned, but you may want to at least report the incident with animal control, but decline to press charges or anything.