What did Hyde do to the girl and how is it he got away with it?

Hyde maliciously trampled an eight-year old girl who was out to fetch a doctor. After apprehending the man, Enfield, the doctor, and the family of the girl decided that, instead of sending for the police, they would blackmail the man to give one hundred pounds to the girl's family. Amenable, the mysterious man disappeared behind the strange door that Utterson and Enfield had encountered. He returned with ten pounds in gold and a check signed by a very respectable third party, Dr. Henry Jekyll.