Today the United States Supreme Court decided Navarette v. California, upholding a California court's determination that a traffic stop of Navarette's truck — which, as it turned out, contained drugs — was supported by reasonable suspicion, and therefore constitutional. The opinion is here. It's a 5-4 decision, with Justice Thomas writing the majority opinion and Justice Scalia writing the dissent. It should have gone the other way.

The issue at hand is the power and reliability of anonymous tips. Here the California Highway Patrol received an anonymous tip through a 911 dispatcher that a silver Ford 150 pickup on a particular highway had run the tipster off the road. The CHP saw a truck matching the description on the highway and stopped it on suspicion of drunk driving — but did not first observe the truck doing anything illegal or reckless. In fact, the cops followed the truck for five miles without observing any traffic violations. The cops approached the truck and (allegedly) smelled marijuana, which led to a search and the discovery of a substantial amount of marijuana in the truck bed.

The Supreme Court has found that the Fourth Amendment permits brief, investigative stops of vehicles based on reasonable suspicion alone — that is, a "particularized and objective" basis to believe some crime is being committed. That's not new. Nor is it new that an anonymous tip can form part of the basis for reasonable suspicion or probable cause — if the tip is corroborated.

What's novel here is that the majority agrees that reasonable suspicion can be premised entirely on a functionally anonymous tip.1 Traditionally the key to corroboration has been confirmation of incriminating details, not details that any observer could make about a innocent subject. So, for instance, if you call in an anonymous tip that I am running a meth lab in my blue house on the corner, and the cops confirm that I have a blue house on the corner, those details are not meaningfully corroborative. If the cops find evidence of witnesses seeing me move precursor chemicals into my blue house on the corner, that's meaningfully corroborative. Here, the police observed no erratic driving or other corroboration of meaningful facts. In fact, they observed five minutes of unremarkable driving. The only corroboration was the innocent fact of the truck being present on the highway.

The majority uses sophistry to turn innocent facts into facts that corroborate the anonymous typster:

By reporting that she had been run off the road by aspecific vehicle—a silver Ford F-150 pickup, license plate 8D94925—the caller necessarily claimed eyewitness knowledge of the alleged dangerous driving. That basis of knowledge lends significant support to the tip’s reliability. . . . . A driver’s claim that another vehicle ran her off the road, however, necessarily implies that the informant knows the other car was driven dangerously. . . . There is also reason to think that the 911 caller in this case was telling the truth. Police confirmed the truck’s location near mile marker 69 (roughly 19 highway miles south of the location reported in the 911 call) at 4:00 p.m.(roughly 18 minutes after the 911 call). That timeline of events suggests that the caller reported the incident soon after she was run off the road. That sort of contemporaneous report has long been treated as especially reliable. . . . . Another indicator of veracity is the caller’s use of the 911 emergency system. See Brief for Respondent 40–41,44; Brief for United States as Amicus Curiae 16–18. A 911 call has some features that allow for identifying and tracing callers, and thus provide some safeguards against making false reports with immunity.

The majority is turning three things into corroboration here: (1) the fact that the person claimed something happened immediately after it allegedly happened, (2) the fact that a person predicted that a particular car would be on a particular highway, and (3) the fact that the person called 911 and made the claim. But the 911 caller could have claimed anything — that someone was pointing a rocket launcher out the window of the truck, that someone was stabbing a nun in the back of the truck — and gotten the same result. (1) and (3) are just restating the premise "we got an anonymous tip about this," and (2) is a purely innocent fact that any public observer could know. This approach renders the concept of corroboration almost meaningless by making calls to 911 about highway behavior effectively self-corroborating. If I want to call 911 and report that you are weaving in and out of traffic and appear drunk, under this decision, I just created reasonable suspicion to stop you. The cops can pull you over without observing you driving oddly at all — in fact, they can stop you even if they follow you for five minutes and you are driving perfectly.

Justice Scalia's dissent is thorough and merciless, as it should be. Here's how he ends it:

The Court’s opinion serves up a freedom-destroying cocktail consisting of two parts patent falsity: (1) that anonymous 911 reports of traffic violations are reliable so long as they correctly identify a car and its location, and (2) that a single instance of careless or reckless driving necessarily supports a reasonable suspicion of drunkenness. All the malevolent 911 caller need do is assert a traffic violation, and the targeted car will be stopped, forcibly if necessary, by the police. If the driver turns out not to be drunk (which will almost always be the case), the caller need fear no consequences, even if 911 knows his identity. After all, he never alleged drunkenness, but merely called in a traffic violation—and on that point hisword is as good as his victim’s. Drunken driving is a serious matter, but so is the loss of our freedom to come and go as we please without police interference. To prevent and detect murder we do not allow searches without probable cause or targeted Terry stops without reasonable suspicion. We should not do so for drunken driving either. After today’s opinion all of us on the road, and not just drug dealers, are at risk of having our freedom of movement curtailed on suspicion of drunkenness, based upon a phone tip, true or false, of a single instance of careless driving.

Justice Scalia is right. This decision waters down corroboration to the point that it is meaningless, effectively making any anonymous tip of a driver's behavior sufficient to justify a traffic stop. That's a bad result.

See also Jonathan Adler.

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