Which section of a supplementary report explains any updates on the investigation?

The correct choice focuses on the outcome section, as it is specifically designed to convey any updates regarding the investigation. In a supplementary report, this section serves to capture the most recent developments, findings, or conclusions that have emerged since the initial report. It allows for a clear and concise presentation of what has transpired in the case, ensuring that all parties involved are informed of any progress or changes that may affect ongoing proceedings.

In contrast, the summary section typically offers an overview of the initial report's content rather than updates. The background section provides context and relevant history pertaining to the case but does not detail new information or developments. The facts section lays out the objective details of the incident at hand but lacks the analytical or outcome-focused perspective that follows the unfolding of the investigation. Therefore, the outcome is the most appropriate section to refer to for updates on the investigation's status and findings.