Which of the following roles specifically investigates crimes without revealing their identity?

The choice of "Undercover" is the most accurate response for the role that investigates crimes without revealing their identity. Undercover operatives are specifically tasked with operating in a covert manner, often infiltrating criminal organizations or activities to gather intelligence and evidence while maintaining a false identity. This secrecy allows them to gain the trust of those involved, facilitating the gathering of crucial information that might otherwise be inaccessible.

In contrast, while detectives and investigators also play essential roles in the criminal justice system, they typically conduct their work openly and do not operate under a guise. Detectives usually work in an official capacity within law enforcement agencies and interact with the public and suspects without the necessity for concealment. Likewise, field operatives can refer to various roles within law enforcement or security that may not involve undercover operations specifically. Thus, the undercover role is uniquely defined by its requirement for anonymity and deception, making it the correct choice in this context.