In the context of formal criminal justice, which scenario would be categorized as "investigation"?

In the context of formal criminal justice, the scenario that accurately represents "investigation" is when a detective reviews case files. This activity involves examining existing information, evidence, and prior investigation reports to piece together elements of a case, identify leads, and develop a better understanding of the circumstances surrounding a potential crime.

Investigation is a critical phase in the criminal justice process, where law enforcement seeks to gather evidence and information to determine whether a crime has occurred, identify suspects, and prepare for prosecution. By reviewing case files, detectives can identify gaps in evidence, ascertain witness credibility, and formulate strategies for further inquiry or interviews.

The other scenarios involve actions that occur after or during the crime response phase, rather than direct investigative activities: individuals are detained following court proceedings, officers may act upon witnessing a crime, and witness testimony is a part of the trial process rather than the investigation itself. Thus, the detective's review of case files most appropriately encapsulates the essence of an investigative function in criminal justice.