State v. Christopher E. Betow, 226 Wis.2d 90, 593 N.W.2d 499 (Ct. App. 1999)
For Betow: James C. Murray.
There is no question that a police officer may stop a vehicle when he or she reasonably believes the driver is violating a traffic law; and, once stopped, the driver may be asked questions reasonably related to the nature of the stop-including his or her destination and purpose. … Stated another way, the scope of questions asked during an investigative stop must bear a reasonable relationship to the reasons for which the stop was made in the first place. United States v. Brignoni-Ponce, 422 U.S. 873, 881 (1975).
Once a justifiable stop is made-as is the case here-the scope of the officer’s inquiry, or the line of questioning, may be broadened beyond the purpose for which the person was stopped only if additional suspicious factors come to the officer’s attention-keeping in mind that these factors, like the factors justifying the stop in the first place, must be “particularized” and “objective.” United States v. Perez, 37 F.3d 510, 513 (9th Cir. 1994). If, during a valid traffic stop, the officer becomes aware of additional suspicious factors which are sufficient to give rise to an articulable suspicion that the person has committed or is committing an offense or offenses separate and distinct from the acts that prompted the officer’s intervention in the first place, the stop may be extended and a new investigation begun. The validity of the extension is tested in the same manner, and under the same criteria, as the initial stop.
The court goes on to determine that the police lacked reasonable suspicion, hence the detention / questioning after fulfilling the stop’s purpose was unlawful.