What should I do if my son was severely attacked by a dog?

My son was attacked by a dog with excessive force. The dog attacked him in the backyard while surrendering cops were not in vicinity. Witnesses in the home were trying to hit dog off my son and shook my son like a rag doll exposing and cutting through muscle and bone. He got 38 stitches in leg and 20 in buttocks area. I'm really looking for a pro bono attorney or if we have a strong case to get paid if we win.