Which of the following is NOT a reason an investigation would require surveillance?

Surveillance is primarily used in investigations for gathering evidence, monitoring activities of suspects, and observing their interactions and behaviors. Each of the other options reflects a function where surveillance would play a critical role.

Gathering physical evidence often necessitates surveillance, especially in cases where materials or actions need to be documented surreptitiously to maintain the integrity of the evidence. Monitoring a suspect's daily activities is a direct application of surveillance, as it allows investigators to observe patterns that could lead to uncovering further evidence or intents behind a suspect's actions.

Identifying the suspects behind financial fraud may involve surveillance as part of a broader investigative approach, but it often relies more on the analysis of documents, transactions, and electronic trails rather than direct observation of physical actions or activities. This illustrates that although surveillance may help, it's not the primary method for identifying suspects in financial fraud cases. Consequently, conducting interviews with witnesses does not involve surveillance at all, as it requires direct interaction rather than observation. This distinction establishes why identifying suspects through surveillance is less fitting compared to the other surveillance-related activities.