"When hiring investigators, employers are looking for candidates with top-notch observational, communication, and problem solving skills. In an interview, you'll want to demonstrate that you are a critical thinker with strong research abilities and an in depth knowledge of the law. The precise questions you'll be asked will depend on the type of investigation you are looking into, so make sure to do your homework on your employer's line of work."
Tell me how you would conduct an interview of a reference for security clearance.
Identity of reference, determine scope of relationship, ask questions to verify they know the person, ask the designated questions.