My puppy was attacked yesterday....?

We were at a public dog festival in the area, where lots of people brought lots of different dogs. All of the dogs were very well behaved and it was an extremely pleasant time until out of nowhere a fullsize adult dog (mix breed, possible german shepard, pittbull, mastiff), grabs my puppy from behind and lifts her off the ground sinking his teeth into her. She had 4 puncture wounds, 2 of which were where 2 teeth connected below the skin forming a pocket. She now has a piece of gauze running through her back which we have to flush twice a day and she is on 3 medications for her injuries. I got the contact information from the owner and found that he has a website chronicaling all the dogs past troubles in which it's attacked 2 other dogs and a person. One attack was self described as "very brutal." This guy should have never had his dog out in public. I am going to try and get him to pay the medical cost($281) without involving the authorities, but I feel compelled to get them invovled because this dog obviously should never be allowed to be in public. I don't want the dog put down, but this owner needs to be taught a lesson. He knew his dog was very violent and still took it into a situation it obviously couldn't handle. Now my puppy is suffering the consequenses of his moronic actions. How should I handle this situation?