Can your friend identify these yahoos in order to A) prosecuted for criminal trespass and simultaneously B) sue in small claims court for property damages.
Of course if these people made the doctor's life so unbearable he had to move, your friend may suffer a similar problem.
Problem with that is when they pay their 100 dollar ticket then they come after you harder. Nice to come home and find your house vandalised or your dog dead. I say shoot them. I have learned my lesson with formal complaints to the police.