What is necessary for a Terry stop to be valid?

For a Terry stop to be valid, law enforcement officers must have reasonable suspicion supported by articulable facts that a person is involved in criminal activity. This standard is lower than probable cause, which is required for arrests or obtaining search warrants.

Reasonable suspicion allows officers to briefly detain a person to investigate potential criminal activity. The suspicion must be based on specific and articulable facts rather than vague hunches or unparticular beliefs. This principle was established in the landmark case Terry v. Ohio, where the Supreme Court ruled that the need to protect officer safety and prevent crime justified a limited form of police detainment and searches.

In contrast, probable cause, which involves a higher threshold, is necessary for arrests or issuing warrants, thus making other choices incorrect for the context of a Terry stop. No witness testimony or arrest warrant is required for such a stop, aligning with the principle of reasonable suspicion as the foundational requirement.