What can Animal Control do for me?

My family has owned pitbulls for many years. They have been trained well and have been the best companions I've ever known. A little over a year ago, my brother decided to adopt a pitbull. He did not have the dog neutered or trained properly, and beats the dog frequently when he misbehaves. My brother also has a one-year old son who is just learning to walk. This dog has bitten a few people and acts out frequently. My brother responds by punching the dog to the point of the dog whelping and cowering. This makes me sick to my stomach but I don't know what to do about it. I want to call an animal control officer, but I'm afraid they won't see the abuse since the dog has adequate shelter/food, etc. I'm also afraid that the dog will be put to sleep if they see how angry he is. This is still a very young dog and I feel that he can be rehabilitated with the proper trainers. Please give me any advice you can, I don't want a young child getting hurt or a young dog having his life cut short because of my brother's idiocy.