According to the IIA's Fraud and Internal Audit position paper1, internal auditors should not investigate fraud unless they have the specific experience and expertise required to do so. Therefore, the most appropriate option for the chief audit executive is to appoint an independent fraud investigation specialist to work with the selected internal auditors. This will ensure that the investigation is conducted in a professional and ethical manner, and that the evidence is not compromised or tainted. The other options are not suitable because they do not address the immediate need for fraud investigation expertise, and they may expose the organization to legal or reputational risks.