People v. H.J
In People v. H.J., 931 P.2d 1177 (Colo. 1997) the court determined that an officer may request identification of passengers in a car stopped for a traffic violation where there is a reasonable suspicion that the car has been stolen or that there is other criminal activity occurring or about to occur.
The officer's reasonable suspicion in H.J. was supported by the fact that there, no one in the vehicle could produce registration papers for it.
The court held that, based on that suspicious circumstance, the officers could reasonably infer that the passengers in the vehicle were involved in stealing the vehicle, and therefore, could be asked for identification.
The court, however, specifically declined to address whether a seizure occurs where the officer does not have probable cause or a reasonable suspicion that a passenger in a vehicle stopped for a traffic violation is engaged in criminal activity.