According to IIA guidance, any additional roles beyond traditional audit functions, such as being responsible for risk management and investigation, must be explicitly defined in the internal audit charter. This document, approved by senior management and the board, delineates the scope and responsibilities of the internal audit function, ensuring clarity and proper governance. Thus, if the internal audit charter stipulates such roles, it justifies the CEO's decision.
IIA Standard 1000 - Purpose, Authority, and Responsibility

The responsibility of the chief audit executive (CAE) to maintain organizational independence is fulfilled by developing and submitting an annual budget and resource plan to the board for approval. By doing so, the CAE ensures that the internal audit activity has the necessary resources to operate effectively without undue influence from management. This process upholds the independence and objectivity of the internal audit function, as it allows the board to oversee and approve the resources needed for the audit activity, thus preventing potential conflicts of interest and ensuring the audit function remains free from managerial interference.
The IIA's International Standards for the Professional Practice of Internal Auditing (Standards) - Standard
1110: Organizational Independence.
The IIA's Practice Guide on Maintaining Internal Audit Independence.

The effectiveness of the control environment is a fundamental aspect that internal auditors must consider to ensure a comprehensive assessment of the adequacy of controls. The control environment sets the tone at the top and is the foundation on which the rest of the control structure is built, influencing the effectiveness and robustness of specific controls.
Institute of Internal Auditors (IIA) - International Standards for the Professional Practice of Internal Auditing

An effective continuing professional education (CPE) program for internal auditors involves ongoing development and engagement with the broader professional community. By encouraging auditors to volunteer and support research work of the local professional institute, the CAE promotes professional growth, knowledge sharing, and staying current with industry best practices and emerging trends. This practice not only enhances the auditors' skills and knowledge but also fosters networking and professional development opportunities.
The IIA Standards: Standard 1230 - Continuing Professional Development: "Internal auditors must enhance their knowledge, skills, and other competencies through continuing professional development." IIA Practice Guide: "Continuing Professional Education (CPE)": Highlights the importance of engagement with professional bodies and continuous learning as part of an effective CPE program.

Incorrect acceptance risk refers to the risk that an auditor concludes that a financial statement assertion is not materially misstated when, in reality, it is. This type of risk is particularly relevant when performing substantive testing on balances such as inventory, where the auditor uses sampling to draw conclusions about the entire account balance.
Auditing standards regarding audit sampling and risk assessment, including the concepts of Type I and Type II errors in auditing.