State v. Richardson
In State v. Richardson, 156 Wis. 2d 128, 137, 456 N.W.2d 830 (1990), the supreme court concluded that an anonymous tip and the verification of its innocent details provided the police with reasonable suspicion to conduct an investigatory stop. See id. at 144.
The court held that the "corroborated actions of the suspect ... need not be inherently suspicious or criminal in and of themselves.
Rather, the cumulative detail, along with reasonable inferences and deductions which a reasonable officer could glean therefrom, is sufficient to supply the reasonable suspicion that crime is afoot and to justify the stop." 156 Wis. 2d at 142.
The Richardson court identified two principles that courts are to consider in assessing the reliability of an anonymous tip.
First, "the greater the amount, specificity and uniqueness of the detail contained in an anonymous tip, the more likely it is that the informant has an adequate basis of knowledge." Id.
Second, verification of the future predictions of the suspect's behavior is important "to avoid investigative stops based on minimal facts that any passerby or resident on the street could enunciate." Id.
Under the second principle, when significant portions of an anonymous tip are corroborated by the police, an inference arises that the anonymous caller is truthful and that the caller is "more probably than not correct as to the ultimate fact of criminal activity." 156 Wis. 2d at 142-143.