Internships are available from many police departments and federal agencies. Some offer internships for high-school students. These programs offer limited training and ride-alongs with police officers. They teach the qualities and skills necessary for entering the police academy upon graduation or upon reaching a minimum age. In fact, many high-school students apply and are sworn into the departments in which they intern. Most federal agencies offer internships to college students. Each agency has its own requirements, so research the position before applying.

It's also possible to obtain an internship from an established PI company. Companies train investigators in different ways. Some have classes that new employees must attend while others pair the newbie with an experienced investigator for a time. Requirements vary from company to company, but the practice of on-the-job training isn't unusual. One-person operations or small firms may work with other investigators or firms they trust. In this way, a small company isn't forced to turn down jobs that require more manpower than it possesses. These companies may be willing to take on a trainee as a contract worker. Contracting also saves money; small firms can't afford to keep investigators on a payroll while they wait for clients.

Working with an accountant can be a type of on-the-job training. Most people with no accounting experience can find themselves in trouble by not understanding bookkeeping and tax requirements. Therefore, the smart business owner will hire professionals to handle these things, but she will also become a student of all that she does not know. While the investigator is better served by doing the work she is familiar with, she must also protect herself from being taken advantage of by others. Pay professionals to do what they do best, but learn all you can in order to provide oversight.