Which evidence can help locate blood stains during an investigation?

When investigating a crime scene, maintaining meticulous records is crucial for understanding and retracing the steps taken during the investigation. Notes on the process used to locate blood stains provide context and detail about the techniques employed, such as the application of luminol or other reagents, the use of ultraviolet light, or specific patterns of searching that might indicate the presence of blood. These notes not only aid in verifying the accuracy and reliability of the findings but also serve as a documented method that can be referenced in court or by other investigators in future cases.

Video footage, while potentially valuable for visual documentation, does not actively assist in the methodical approach required to locate blood stains. Eyewitness testimony may offer some insights or context but is not a reliable method for forensic analysis since human memory can be faulty. The first-hand account of the investigator's process provides a clear and systematic guide that is essential for both the current investigation and future reference, thus making it the most appropriate choice in this scenario.