Final answer:
The least effective approach in this scenario would be attempting to get the suspected individual to confess. Instead, the internal auditor should strive to maintain objectivity and gather information through other means.
Step-by-step explanation:
The least effective approach in this scenario would be option C, attempting to get the suspected individual to confess. While it may be tempting to try and elicit a confession directly, it can often be difficult to achieve and may lead to a defensive response or denial from the suspected individual.
Instead, an internal auditor should strive to maintain objectivity and gather as much information as possible through options A, B, and D. Taking the role of one seeking the truth (option A), asking each individual to prepare a written statement explaining their actions (option B), and listening carefully to what each interviewee has to say (option D) are all effective approaches that can provide valuable insights and evidence.