What is a key requirement for an investigatory stop to be lawful?

A key requirement for an investigatory stop to be lawful is the presence of reasonable suspicion of criminal involvement. This legal standard allows law enforcement officers to stop and briefly detain a person for questioning if they have specific and articulable facts that lead them to believe that the individual may be involved in criminal activity. This is a lower threshold than probable cause, which is necessary for an arrest, making it easier for officers to engage in limited detainment for further investigation.

In practice, reasonable suspicion can be based on observations of unusual behavior, knowledge of recent crimes in the area, or other specific circumstances that alert an officer to potential criminal activity. It is essential for maintaining a balance between law enforcement's ability to prevent and investigate crime while also protecting individuals’ rights against arbitrary stops and detentions.

Clear evidence of a crime, consent from the individual, or testimony from witnesses would typically apply in different contexts, such as making an arrest or when obtaining a search warrant, but they do not meet the specific requirement for an investigatory stop. Reasonable suspicion is the foundational principle that allows officers to act on their instincts and experience to prevent crime effectively.