I'm not sure an investigator is the most productive course. If it was me, I'd start with a Cease and Desist letter from a lawyer. Cost: about 2 billable hours.

I'm not sure an investigator is the most productive course. If it was me, I'd start with a Cease and Desist letter from a lawyer. Cost: about 2 billable hours. If that fails, since there is, in fact, a law being broken, and now the creeper has ignored a C&D, get a court order. No need to involve police, they can continue writing speeding tickets and tending to other urgent matters. If the creeper ignores the court order, then see if you can get a bench warrant issued. Although, in this case, it sounds like the person is mentally ill -- what you can do about that varies greatly from state to state.