Dog owner negligent,dog causing nuisance what can be done

Dear sir, I am a resident of ccwo colony dhanbad and a owner of labrador. There is anothe dog owner in the vicinity with a doberman who has prior records of biting etc and he practically takes it unleashed most of the time. On one such fateful afternoon while i was walking with my dog he attacked us and maulled my dog real bad. His owner calmly followed him as if taking pride in what has happened. He just said the dogs fought. I just dont understand how can somebody be so negiligent and purposefulky unleash deadly dogs on others pets and behave as if it was completely legal. Please help what can i do.