Which document remains with the oil sample and cannot be a photocopy?

The correct answer is the Chain of Custody, which is crucial for maintaining the integrity and admissibility of evidence in legal proceedings. This document tracks the handling of the oil sample from the moment it is collected until it is analyzed. It contains details about who collected the sample, where it was stored, and each individual who has handled it throughout the process.

The Chain of Custody must remain with the sample itself because it provides a legally binding record that can demonstrate the sample has not been tampered with or altered in any way. If a photocopy were to be used instead of the original, it could lead to questions about the integrity of the sample and its analysis.

In contrast, documents like the Letter of Request, Sample Label, and Analysis Report can often be photocopied for various purposes without compromising the legal standing of the original sample. Therefore, the Chain of Custody is unique in its need for the original to ensure the reliability of the sample and its subsequent analysis.