Another type of stop that fits under the definitiion of “investigative detention” is the “Terry stop.” Named after the United States Supreme court case that defined it, a Terry stop is a search limited under Pennsylvania law by reasonable suspicion regarding activites personally observed by the officer and a reasonable belief that the suspect is armed and dangerous. Further, past criminal activity is not enough for the stop; it must be an “immediate” suspicion of current illegal conduct.
The purpose of the Terry stop is to allow an officer to conduct a pat down search to determine whether the person is carrying weapon. The issue is not the discovery of evidence, but to allow the officer to pursue his investigation without fear of violence. Thus, to conduct a Terry stop, the officer must reasonably believe that his safety or the safety of others is threatened. If either the seizure (the initial stop) or the search (the frisk) is found to be unreasonable, the remedy is to exclude all evidence derived from the illegal government activity.
Of course, despite all of the rhetoric regarding officer safety, the “frisk” component has, over the years, morphed into the permitting of a “plain feel” exception to the search warrant requirement in Pennsylvania. Thus, the appellate courts have sustained a seizure where the police, with reasonable suspicion to belief that a person was involved in a drug transaction, felt an object having the “’consistency of a bundle of caps’ [cocaine vials].” However, a frisk is only legal if it is directed toward weapons. The Superior Court has also held that one may not justify a frisk based on a rationale that “guns and drugs go together,” or that one may search items that could not be dangerous (foil, plastic bags, etc.).