Under which circumstance may an officer detain a person in relation to Terry stops?

In relation to Terry stops, an officer may detain a person when there is a reasonable suspicion based on specific behaviors that suggest a person may be involved in criminal activity. This principle comes from the landmark Supreme Court case Terry v. Ohio, which established that officers do not need probable cause to make a stop; rather, they must have a reasonable belief that the individual is engaged in, or about to engage in, criminal conduct based on observable facts or circumstances.

When an officer observes specific behaviors—such as acting unusually nervous, loitering in a high-crime area, or making evasive movements—that can indicate potential criminal behavior, that constitutes reasonable suspicion. This standard is lower than probable cause, allowing officers to briefly detain individuals to ask questions or investigate further, ensuring both public safety and the officer's safety.

The other options do not accurately reflect the legal standard required for a Terry stop. A vague feeling lacks the specificity required for reasonable suspicion, no suspicion at all contradicts the essence of a Terry stop, and merely witnessing a crime is not necessary for all situations; reasonable suspicion provides the legal grounding for the initial stop.