A police officer may stop and briefly detain an individual if he or she has a “reasonable, articulable suspicion” that the individual is committing a crime. Such stops may be based on a citizen’s tip but generally only if there is some corroboration of the tip. For example, Al flags down an officer in his neighborhood and reports Bert just walked by high on drugs. Based solely on the tip, the officer cannot simply approach and grab hold of Bert for questioning. Some additional factor leading the officer to reasonably suspect Bert is under the influence of drugs is required. The officer is permitted to approach and speak to Bert voluntarily but Bert must be free to talk away. However, the situation changes if, for example, the officer sees Bert staggering into the street. Al’s tip could then be considered corroborated and the officer could briefly detain Bert for further investigation.