Which situation represents the need for biological evidence collection?

The situation that indicates the need for biological evidence collection is when hair strands are left on clothing. This is crucial because hair can serve as valuable biological evidence, potentially linking a suspect to a crime scene or victim. Hair can provide DNA that aids in identifying the individual from whom it originated, which is critical in forensic investigations. When hair is found at a crime scene, it can be analyzed for nuclear DNA if the root is intact, or mitochondrial DNA if it is just the shaft, thus offering vital information about the person involved.

In contrast, the other scenarios do not specifically indicate a need for biological evidence collection. Scratched surfaces from a tool might require forensic analysis of tool marks but are not linked to biological evidence. A witness account provides narrative details but does not physically connect to biological evidence. Lastly, a shoe print in the soil is relevant for footprint analysis and comparison but does not involve biological materials; it focuses more on impression evidence rather than biological evidence.