A police officer may stop and briefly detain an individual only when the officer has reasonable suspicion to believe that person is involved in criminal activity. When may an anonymous tip provide the basis for such suspicion?The objective of this article and self-study test is to review the legal framework concerning when an anonymous tip may constitute reasonable suspicion for an investigatory stop. Readers will learn about the case law that governs when a police officer's reliance on an anonymous tip is proper under the Fourth Amendment to the U.S. Constitution. General Principles In what is often referred to as a "Terry stop," a law enforcement officer may perform a brief investigative stop where the officer has a particularized and objective basis for suspecting that the person is involved in criminal activity. See Terry v. Ohio, 392 U.S. 1 (1968). This is known as "reasonable suspicion." On the one hand, a police officer's "hunch" is insufficient to constitute reasonable suspicion. On the other hand, reasonable suspicion does not require the level of information that makes it probable that the person is engaged in a crime. "The standard of reasonable suspicion is less demanding than probable cause not only in the sense that reasonable suspicion can be established with information that is different in quantity or content than that required to establish probable cause, but also in the sense that reasonable suspicion can arise from information that is less reliable than that required to show probable cause." Arburn v. Dept. of Motor Vehicles, 151 Cal. App. 4th 1480 (2007); accord United States v. Sokolow, 490 U.S. 1 (1989). Whether an officer has reasonable suspicion depends upon the totality of the circumstances before the officer. United States v. Cortez, 449 U.S. 411 (1981). It is settled that information offered by others - not just observations made by the officer herself - may provide reasonable suspicion. See Adams v. Williams, 407 U.S. 143 (1972). Whether there is reasonable suspicion in a particular case depends upon, first, the reliability of the information before the officer, and second, whether the content of that information connects the suspect to criminal activity. Reliability A bare anonymous tip, lacking a basis to conclude it is reliable in asserting that a suspect is engaged in criminal activity, does not establish reasonable suspicion. Florida v. J.L., 529 U.S. 266 (2000), provides the leading example. In J.L., an anonymous caller told the police that a young plaid-shirted black male standing at a particular bus stop was carrying a gun. Officers went to the bus stop and saw three black males, one of whom, J.L., was wearing a plaid shirt. The officers observed no gun, nor anything else suspicious. Upon stopping and frisking J.L., officers found a gun in his pocket, leading to charges against him. The Supreme Court held that the firearm must be suppressed as the product of a search invalid under the Fourth Amendment. At the time of the stop, there was nothing about the tip that would render it reliable in identifying criminal activity. Although the tipster correctly identified a black male wearing a plaid shirt at the bus stop, this did not show that the tipster had any reliable knowledge about the gun. Two other U.S. Supreme Court cases have demonstrated the means by which officers may conclude that an anonymous tip is reliable. First, the tip alone could contain information that corroborates its accusation of criminal activity. Second, the tip could predict the future behavior of the suspect in a manner that, once that behavior occurs, demonstrates that the tipster knew about criminal activity. Alabama v. White, 496 U.S. 325 (2000), provides an example of prediction of future behavior. There, an anonymous tipster alleged that a woman would leave a particular apartment at a particular time in a brown Plymouth station wagon with a broken right tail light, and that she would go to a particular motel with an ounce of cocaine inside a brown attachÃ(C) case. The officers then followed a woman who left the apartment driving a vehicle matching the description, and they stopped her near the predicted motel, where they searched and found the cocaine. The Supreme Court held that the tipster's information provided reasonable suspicion because the accurate prediction of the woman's behavior demonstrated the informant had "a special familiarity with [her] affairs," rendering the tip reliable. As "only a small number of people are generally privy to an individual's itinerary," the court in White reasoned, the predicted behavior gave officers reason to believe "not only that the caller was honest but also that he was well informed." More recently, in Navarette v. California, 134 S. Ct. 1683 (2014), the Supreme Court held that officers had reasonable suspicion to conclude that a driver was intoxicated after an anonymous 911 tipster reported that the driver of a silver Ford 150 pickup truck with a particular license plate had run her vehicle off of southbound Highway 1. The court found it significant that the tip itself purported to represent eyewitness knowledge of dangerous driving. The court further reasoned that the caller's reliability was supported when officers spotted the particular truck headed southbound on Highway 1 soon after the call, making the tipster's report contemporaneous with being run off the road. The court relied on hearsay rules that find statements reliable when made shortly after startling events. Navarette, citing, inter alia, Fed. Rule Evid. 803(2) (hearsay exception for "excited utterances"). Finally, the court in Navarette found that the caller's use of the 911 emergency system was a factor supporting the reliability of a tip. Because 911 calls may be recorded, and because there are other ways in which the caller's phone number or cellphone location could be traced, "a reasonable officer could conclude that a false tipster would think twice before using such a system." See also People v. Dolly, 40 Cal. 4th 458, 467 (2007) (indicating that use of the 911 system may support a tip's reliability). Navarette accorded with the reasoning of the California Supreme Court eight years earlier. In People v. Wells, 38 Cal. 4th 1078 (2006), the court held that an anonymous call alleging that a blue van was "weaving all over the roadway" was sufficient to support a stop for reasonable suspicion of drunk driving. Wells, as Navarette, relied on the fact that the caller appeared to have been a percipient witness to conduct indicating drunk driving, as well as that the location of the spotted vehicle indicated that the statement was contemporaneous. See Wells. One difference between the approaches in Wells and in Navarette is that in the former, the California Supreme Court created a special rule for evaluating tips in cases "deemed exigent by reason of possible reckless driving or similar threats to public safety," distinguishing less-pressing situations and concluding that "the grave risks posed by an intoxicated highway driver justified the minimal intrusion of a brief investigatory traffic stop." Wells; see also Dolly (approving of stop based on tip reporting assault with firearm, in part because of the "grave and immediate risk" presented by the particular crime). The U.S. Supreme Court in Navarette did no such balancing and did not indicate that the type of crime alleged affects how the legal principles apply. Criminal Activity For the traffic stop to be constitutional, not only must the anonymous tip be reliable, but the content of the tip must show reasonable suspicion that criminal activity may be afoot. In Navarette, the Supreme Court held that the tip provided reasonable suspicion of drunk driving. The reported conduct - running another vehicle off the road - resembled "paradigmatic manifestations of drunk driving" and demonstrated that the driver was "likely intoxicated." Though there were other possible explanations for the reported behavior (a distracted driver, for instance), the reasonable suspicion standard does not require that officers rule out the possibility of innocent conduct. Ibid., citing United States v. Arvizu, 534 U.S. 266 (2002). The court in Navarette noted that if the reported conduct were different - driving slightly over the speed limit, for example - it would be too tenuously connected to drunk driving to support a stop. Navarette also noted that the 911 call consisted of "more than a conclusory allegation of drunk or reckless driving. Instead, she alleged a specific and dangerous result of the driver's conduct: running another car off the highway." Interestingly, the court in Navarette observed that extended observation of an allegedly drunk driver might eventually dispel reasonable suspicion of intoxication, if officers observed nothing remiss. But the fact that officers observed the suspect driving for just five minutes without incident did not do so in Navarette. Conclusion An anonymous tip alone may provide reasonable suspicion for a police stop, so long as the tip reliably shows that the suspect is engaged in criminal activity. Though the tip in J.L. failed to support such suspicion, in both White and Navarette, the U.S. Supreme Court upheld stops based on anonymous tips. Both cases, however, were split decisions in which the majority noted that it was deciding a "close case" after reviewing the totality of the circumstances. Thus, determinations of whether an anonymous tip provides reasonable suspicion typically will turn on a close examination of all the facts at the time of the stop.