The U.S. Supreme Court Considers Anonymous Tips: Part One of a Two-Part Series of Columns

Posted in: Constitutional Law

This is Part One in a two-part series of columns.  Part Two in the series will appear here on Justia’s Verdict on Wednesday, October 23. –Ed.

This term, the U.S. Supreme Court will consider the case of Navarette v. California, which asks whether police may lawfully stop a vehicle for reckless driving on the basis of an anonymous tip.  The question is difficult, because the Court has long had an ambivalent relationship both with relying on anonymous tips, and with how best to define the “reasonable suspicion” that permits police to perform seizures without probable cause.  This column considers Navarette in light of that ambivalence.

Using Informants to Justify Arrests and Stops

Under the Fourth Amendment, before arresting someone, police must have probable cause to believe that the person they wish to arrest has committed a crime.  Police may acquire such probable cause by directly witnessing the suspect committing the offense, or by directly observing circumstantial evidence of the crime (such as a suspect’s running from the scene).  However, when police investigate a crime that has already occurred, they frequently must rely on the observations of other people to substantiate the level of suspicion necessary to justify an arrest (or a search, which also generally requires probable cause).  These other people are sometimes known as informants.

Like the police, informants might directly witness the commission of a crime, or might instead make observations from which they infer that a particular suspect was involved in a crime.  When police officers rely on an informant’s observations instead of on their own, police must assess the trustworthiness of the informant’s tip.  Such an assessment generally takes into account two factors, to a greater or lesser extent:  How credible and believable is the informant?; and How did the informant come to have the information that he or she is passing along to the police?

Police may conclude that an informant is credible because he has a history of giving good tips to law enforcement, or because she is an apparently truthful citizen coming forward and identifying herself, claiming to have seen someone commit an offense.  The Supreme Court declared in Illinois v. Gates that probable cause based on an informant’s tip calls for a “totality of circumstances” analysis, one that takes an informant’s credibility and basis of knowledge into account, but that also does not rigidly insist on satisfying both of these prongs.

Reasonable suspicion works similarly.  For police to perform a stop—a brief detention that falls short of an arrest requiring probable cause—they must have reasonable suspicion to believe that the person to be stopped has committed, or is about to commit, a criminal act.  Reasonable suspicion is a quantity of suspicion that is less than probable cause (which, in turn, is less than a preponderance of the evidence).  In Terry v. Ohio, the U.S. Supreme Court indicated that articulable suspicion (which is essentially reasonable suspicion) to believe that criminal activity may be “afoot,” suffices to detain the suspect for a brief period to either confirm or dispel the suspicion.

As in the case of probable cause for arrest, police may rely on their own observations or on those of an informant, and police (and later, courts) will assess whether the police were justified in relying on the informant, given some mix of the informant’s credibility and her basis for knowing what she claimed to know.  The Supreme Court said further, in Alabama v. White, that when police use an informant’s tip as a basis for reasonable suspicion, the standard to be applied parallels that which applies for probable cause, but the standard requires both quantitatively less evidence and qualitatively less trustworthy evidence, as well.

Arrests Versus Stops

When the Supreme Court first decided Terry v. Ohio, there appeared to be an important substantive difference between arrests and stops, a difference made more explicit in the concurring opinion of Justice Harlan:  Stops on the basis of reasonable suspicion represented a departure from the “probable cause” norm, and such stops were justified in part because of the important governmental interest in protecting the public and the officers themselves from danger before any crime has occurred.  In Terry itself, several men were allegedly “casing” an establishment, seemingly preparing to commit a crime.  To wait for probable cause to develop would have meant allowing the offense to take place, an undesirable state of affairs.  Therefore, even though police ordinarily need probable cause before detaining anyone, the interest in stopping crime before it starts justified a less demanding standard, one more appropriate to a crime that has yet to occur—a crime that is “afoot.”  That less demanding standard was reasonable suspicion.

In the years following Terry, however, Supreme Court decisions eroded the apparent substantive distinction between the reason for arrests and the reason for stops.  The Court specifically held in United States v. Hensley that if police have reasonable suspicion to believe that a suspect has already completed a felony, they may briefly detain the suspect, just as they could do if they had reasonable suspicion to believe that he was about to violate the law.  As a formal matter, then, reasonable suspicion has become the standard for what police need for a stop, because stops are less intrusive than arrests, and stops thus call for less in the way of foundation than do arrests.


As mentioned above, a police officer who knows an informant personally can make an informed judgment about whether, and to what extent, the informant’s tip is trustworthy.  If the informant has given truthful information in the past, this counsels in favor of believing him or her now.  Furthermore, if police are in a position to corroborate some of what the informant says, then that corroboration—even in the absence of a track record on the informant’s part—can counsel in favor of believing the informant’s as-yet-uncorroborated claims about a suspect’s criminality as well.  And knowing who the informant is provides a check against dishonesty, because police can hold a lying informant accountable for his or her deceptions, after the fact.

Professional informants, though they may have the advantage of a “good track record,” may also, however, hold the position of police informant because they have themselves earlier committed some crime and are hoping for lenient treatment in return for providing tips.  This is not uniformly a bad thing, of course, as an informant whose tips prove worthless is unlikely to curry favor with law enforcement.  Nonetheless, a prior criminal history (perhaps in the same illegal business in which the current suspect stands accused of participating) can somewhat undermine an informant’s credibility.

By contrast, the new and non-“professional” informant who lacks the sort of criminal history that gives rise to an obvious motive to curry favor with the police, is presumptively credible.  For example, if you were to approach a police officer and provide information about your observations of a neighbor’s criminal activities, the police officer would be able to rely on your statements (assuming the statements were internally coherent and plausible) without necessarily having to otherwise affirmatively verify that you are a credible person.

The anonymous informant, however, lacks the advantages of both the professional and the lay informant, just described.  By definition, anonymous informants lack a “track record,” and they also cannot be presumed to be credible, since police have no means of gauging their possible motives for making false accusations or of holding them accountable for false tips.  On their face, such informants would thus appear to have almost no credibility.  Yet the Supreme Court has allowed for the use of anonymous informants’ tips in substantiating both probable-cause and reasonable-suspicion determinations, in Illinois v. Gates and Alabama v. White, respectively.

In Gates, an anonymous informant wrote a letter to the police claiming that Lance and Sue Gates were selling drugs, hiding $100,000 of drugs in their basement, bragging about not having to work, and planning a trip to Florida to buy over $100,000 worth of drugs.  The letter specified the approximate timing for the trip, as well as some other details of the couple’s regular travel arrangements.  The police corroborated some of these details—including the timing of the upcoming trip as well as its initiation in real time, through their own investigation, and ultimately acquired a warrant to search the couple’s car and home, where they found drugs, weapons, and other contraband.

The Supreme Court held that the combination in Gates of the anonymous informant’s tip and police corroboration of some of the information that the tip provided were sufficient to make out probable cause to justify the issuance of the search warrant.  This was true, moreover, despite the fact that what the police corroborated were primarily innocent sorts of details—in other words, details that did not (in the absence of the criminal accusations) necessarily point to criminal activity.

As we see from examining these precedents, anonymous tips can play an important role in providing the justification for detaining and arresting suspects, respectively.  At the same time, such tips give rise to legitimate credibility concerns that might otherwise be absent or far less salient if police were relying on a known, accountable informant in whose tips they had reason to trust.  In Part Two of this column, which will appear here on Justia’s Verdict, I will turn to the specific facts of Navarette as well as recent precedent from the Supreme Court, to help discover how the Court might best think about the anonymous tip that led to the convictions of two men now seeking reversal from the high court.