The most important factor in the internal audit activity's independence specified in an internal audit charter is the description of the internal audit activity's reporting structure. This element defines to whom the chief audit executive reports functionally and administratively, which is critical to ensuring the independence and objectivity of the internal audit function from management and other potential sources of bias.
The IIA's International Standards for the Professional Practice of Internal Auditing on independence and objectivity.

Demonstrating due professional care during an assurance engagement, according to IIA standards, includes systematically planning, executing, and documenting audit procedures. This ensures that all aspects of the engagement are covered comprehensively and that findings and conclusions are well-supported and credible.
This approach aligns with the IIA's definition of due professional care, which emphasizes thoroughness and accuracy in the audit process.
The Institute of Internal Auditors (IIA) - International Standards for the Professional Practice of Internal Auditing.

The personnel development practice applied in this situation is 'outbound rotation.' This practice involves temporarily assigning staff from their usual roles into other departments or functions within the organization to gain a deeper understanding and knowledge of those areas. In this case, the internal auditor working in the procurement department to learn about the procurement process is a classic example of an outbound rotation.
Human resources management practices and IIA guidelines on staff development

In a consulting engagement, it is generally acceptable and often expected that the engagement client will determine the scope of the engagement to ensure that the consulting services meet their specific needs. This collaborative approach helps in aligning the audit services with the desired outcomes of the client while maintaining the flexibility needed in consulting engagements. However, the internal auditor must ensure that such scope setting does not impair their objectivity.
The IIA's Practice Advisories on Consulting Engagements

When a potential fraud instance is identified, the chief audit executive (CAE) appoints a lead investigator to manage the investigation. The next critical step is to determine the competencies needed for the investigation and assess whether the team members have any conflicts of interest. This ensures that the investigation team has the appropriate skills, knowledge, and objectivity to handle the case effectively. Ensuring there are no conflicts of interest is vital to maintain the integrity and credibility of the investigation process.
IIA Practice Guide: Internal Auditing and Fraud
IIA Standard 1210: Proficiency
IIA Standard 1120: Individual Objectivity