In State v. Williams, 225 Wis. 2d 159, 168, 591 N.W.2d 823 (1999), the Court held that an anonymous tip supplied by a citizen informant, lacking in prediction but describing a crime in progress, may be accorded some weight in an officer's consideration of reasonable suspicion, even though it does not predict future activity. In Williams the caller to 911 reported that some people in a vehicle which he described, was parked next to his apartment building and were selling drugs. 225 Wis. 2d at 163-164. The court concluded that even though the caller did not give his name, the officers who arrived at the scene after receiving a radio dispatch based on the call, had reasonable suspicion to conduct an investigatory stop of the occupants of the vehicle. See id. at 183. In State v. Williams, an anonymous 911 telephone caller reported suspected drug dealing in a van parked in a driveway adjacent to his residence. The caller provided a description of the vehicle and a general description of the area of the alleged activity. Based upon the reported information, the police responded to the location and discovered drugs, and Williams was charged with possession of cocaine with intent to deliver. See 225 Wis. 2d at 162-166. Williams challenged the sufficiency of the tipster's 911-related information. The trial court held that the information was sufficient, but the court of appeals reversed, holding that the tipster's information failed to reach the requisite level of reasonable suspicion necessary for a stop. See 225 Wis. 2d at 166-67. The supreme court reversed the court of appeals, holding that the tipster's information satisfied the "veracity," "reliability" and "basis of knowledge" factors under the totality of the circumstances test. See 225 Wis. 2d at 174-183. The key question concerning the tipster's "basis of knowledge" is "how does the tipster know the information that he or she is relaying?" Id. at 175. In Williams, the tipster's basis of knowledge was satisfied by the fact that the information provided was contemporaneous with the tipster's observations. See id. In sum, the supreme court announced that an anonymous tip will provide an adequate basis for reasonable suspicion if the innocent details of the tip are corroborated by the facts observed by officers at the scene. Observation of criminal activity is not a prerequisite. See Williams, 225 Wis. 2d at 175. The supreme court reasoned that "the officers' corroboration of the readily observable information supports a finding that because the tipster was correct about the details of these innocent activities, he or she is probably correct about the ultimate fact of criminal activity." Id. In Williams, the court found that the details of an anonymous tip regarding drug--selling activity were sufficiently corroborated to establish reasonable suspicion. See id. at 181-83. An anonymous tipster reported to a 911 operator that persons were selling drugs in a dark blue and burgundy Bronco located in the alley adjacent to the tipster's apartment. See id. at 163-64. Police corroborated the tip. See id. at 165. They arrived in a few minutes and discovered a Blazer, which looks much like a Bronco, of the color and at the location described by the tipster, containing a number of people. See id. In Williams, suspicion was enhanced because the Blazer did not have license plates and one of the defendant's hands was hidden from the view of the police. See id. at 181-82.