How do regional or national Investigative Agencies usually work?

Typically, if you were to reach out to a larger investigative agency, you will be handed over to a case manager who will seek to understand your case and what your overall goal is. Once this is established, he will likely coordinate with one or multiple PIs in different fields in order to obtain the information you are seeking.

These agencies have the advantage of employing several PIs who specialize in several different fields as well as having established relations with multiple contractors who they will bring in on a case by cases basis.