Florida v. Harris

NOTE: Where it is feasible, a syllabus (headnote) will be released, as isbeing done in connection with this case, at the time the opinion is issued.The syllabus constitutes no part of the opinion of the Court but has beenprepared by the Reporter of Decisions for the convenience of the reader. See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.




No. 11–817. Argued October 31, 2012—Decided February 19, 2013


Officer Wheetley pulled over respondent Harris for a routine traffic stop. Observing Harris’s nervousness and an open beer can, Wheet ley sought consent to search Harris’s truck. When Harris refused, Wheetley executed a sniff test with his trained narcotics dog, Aldo.The dog alerted at the driver’s-side door handle, leading Wheetley toconclude that he had probable cause for a search. That search turned up nothing Aldo was trained to detect, but did reveal pseudoephed rine and other ingredients for manufacturing methamphetamine. Harris was arrested and charged with illegal possession of those in gredients. In a subsequent stop while Harris was out on bail, Aldo again alerted on Harris’s truck but nothing of interest was found. At a suppression hearing, Wheetley testified about his and Aldo’s exten sive training in drug detection. Harris’s attorney did not contest the quality of that training, focusing instead on Aldo’s certification andperformance in the field, particularly in the two stops of Harris’s truck. The trial court denied the motion to suppress, but the FloridaSupreme Court reversed. It held that a wide array of evidence was always necessary to establish probable cause, including field performance records showing how many times the dog has falselyalerted. If an officer like Wheetley failed to keep such records, he could never have probable cause to think the dog a reliable indicatorof drugs.

Held: Because training and testing records supported Aldo’s reliability in detecting drugs and Harris failed to undermine that evidence, Wheetley had probable cause to search Harris’s truck. Pp. 5–11.

(a) In testing whether an officer has probable cause to conduct a search, all that is required is the kind of “fair probability” on which “reasonable and prudent [people] act.” Illinois v. Gates, 462 U. S. 213, 235. To evaluate whether the State has met this practical and


common-sensical standard, this Court has consistently looked to the totality of the circumstances and rejected rigid rules, bright-line tests, and mechanistic inquiries. Ibid.

The Florida Supreme Court flouted this established approach bycreating a strict evidentiary checklist to assess a drug-detection dog’s reliability. Requiring the State to introduce comprehensive docu mentation of the dog’s prior hits and misses in the field, and holding that absent field records will preclude a finding of probable cause nomatter how much other proof the State offers, is the antithesis of a totality-of-the-circumstances approach. This is made worse by the State Supreme Court’s treatment of field-performance records as theevidentiary gold standard when, in fact, such data may not capture adog’s false negatives or may markedly overstate a dog’s false posi tives. Such inaccuracies do not taint records of a dog’s performance in standard training and certification settings, making that perfor mance a better measure of a dog’s reliability. Field records may sometimes be relevant, but the court should evaluate all the evi dence, and should not prescribe an inflexible set of requirements.

Under the correct approach, a probable-cause hearing focusing on adog’s alert should proceed much like any other, with the court allow ing the parties to make their best case and evaluating the totality ofthe circumstances. If the State has produced proof from controlled settings that a dog performs reliably in detecting drugs, and the de fendant has not contested that showing, the court should find proba ble cause. But a defendant must have an opportunity to challenge such evidence of a dog’s reliability, whether by cross-examining thetestifying officer or by introducing his own fact or expert witnesses.The defendant may contest training or testing standards as flawed ortoo lax, or raise an issue regarding the particular alert. The court should then consider all the evidence and apply the usual test forprobable cause—whether all the facts surrounding the alert, viewedthrough the lens of common sense, would make a reasonably prudent person think that a search would reveal contraband or evidence of a crime. Pp. 5–9.

(b) The record in this case amply supported the trial court’s deter mination that Aldo’s alert gave Wheetley probable cause to searchthe truck. The State introduced substantial evidence of Aldo’s train ing and his proficiency in finding drugs. Harris declined to challenge any aspect of that training or testing in the trial court, and the Court does not consider such arguments when they are presented for thisfirst time in this Court. Harris principally relied below on Wheetley’s failure to find any substance that Aldo was trained to detect. That infers too much from the failure of a particular alert to lead to drugs,and did not rebut the State’s evidence from recent training and test

Cite as: 568 U. S. ____ (2013) Syllabus ing. Pp. 9–11. 71 So. 3d 756, reversed. KAGAN, J., delivered the opinion for a unanimous Court.

NOTICE: This opinion is subject to formal revision before publication in thepreliminary print of the United States Reports. Readers are requested tonotify the Reporter of Decisions, Supreme Court of the United States, Wash ington, D. C. 20543, of any typographical or other formal errors, in orderthat corrections may be made before the preliminary print goes to press.


No. 11–817



[February 19, 2013]

JUSTICE KAGAN delivered the opinion of the Court.

In this case, we consider how a court should determine if the “alert” of a drug-detection dog during a traffic stopprovides probable cause to search a vehicle. The Florida Supreme Court held that the State must in every casepresent an exhaustive set of records, including a log of thedog’s performance in the field, to establish the dog’s relia bility. See 71 So. 3d 756, 775 (2011). We think that de mand inconsistent with the “flexible, common-sense standard” of probable cause. Illinois v. Gates, 462 U. S. 213, 239 (1983).


William Wheetley is a K–9 Officer in the Liberty County, Florida Sheriff ’s Office. On June 24, 2006, he was on a routine patrol with Aldo, a German shepherd trained todetect certain narcotics (methamphetamine, marijuana,cocaine, heroin, and ecstasy). Wheetley pulled over re spondent Clayton Harris’s truck because it had an expired license plate. On approaching the driver’s-side door, Wheetley saw that Harris was “visibly nervous,” unable to sit still, shaking, and breathing rapidly. Wheetley alsonoticed an open can of beer in the truck’s cup holder. App. 62. Wheetley asked Harris for consent to search the truck,but Harris refused. At that point, Wheetley retrieved Aldofrom the patrol car and walked him around Harris’s truckfor a “free air sniff.” Id., at 63. Aldo alerted at the driver’s-side door handle—signaling, through a distinctive set of behaviors, that he smelled drugs there.

Wheetley concluded, based principally on Aldo’s alert, that he had probable cause to search the truck. His search did not turn up any of the drugs Aldo was trained to de tect. But it did reveal 200 loose pseudoephedrine pills, 8,000 matches, a bottle of hydrochloric acid, two contain ers of antifreeze, and a coffee filter full of iodine crystals—all ingredients for making methamphetamine. Wheetleyaccordingly arrested Harris, who admitted after proper Miranda warnings that he routinely “cooked” metham phetamine at his house and could not go “more than a fewdays without using” it. Id., at 68. The State charged Harris with possessing pseudoephedrine for use in manu facturing methamphetamine.

While out on bail, Harris had another run-in with Wheetley and Aldo. This time, Wheetley pulled Harris over for a broken brake light. Aldo again sniffed the truck’s exterior, and again alerted at the driver’s-side door handle. Wheetley once more searched the truck, but onthis occasion discovered nothing of interest.

Harris moved to suppress the evidence found in histruck on the ground that Aldo’s alert had not given Wheet ley probable cause for a search. At the hearing on that motion, Wheetley testified about both his and Aldo’s train ing in drug detection. See id., at 52–82. In 2004, Wheet ley (and a different dog) completed a 160-hour course in narcotics detection offered by the Dothan, Alabama Police Department, while Aldo (and a different handler) completed a similar, 120-hour course given by the Apopka, Florida Police Department. That same year, Aldo received a one year certification from Drug Beat, a private company that specializes in testing and certifying K–9 dogs. Wheetleyand Aldo teamed up in 2005 and went through another,40-hour refresher course in Dothan together. They alsodid four hours of training exercises each week to maintaintheir skills. Wheetley would hide drugs in certain ve- hicles or buildings while leaving others “blank” to deter mine whether Aldo alerted at the right places. Id., at 57. According to Wheetley, Aldo’s performance in those exer cises was “really good.” Id., at 60. The State introduced “Monthly Canine Detection Training Logs” consistent withthat testimony: They showed that Aldo always found hidden drugs and that he performed “satisfactorily” (the higher of two possible assessments) on each day of train ing. Id., at 109–116.

On cross-examination, Harris’s attorney chose not tocontest the quality of Aldo’s or Wheetley’s training. She focused instead on Aldo’s certification and his performance in the field, particularly the two stops of Harris’s truck.Wheetley conceded that the certification (which, he noted,Florida law did not require) had expired the year beforehe pulled Harris over. See id., at 70–71. Wheetley also acknowledged that he did not keep complete records of Aldo’s performance in traffic stops or other field work;instead, he maintained records only of alerts resulting in arrests. See id., at 71–72, 74. But Wheetley defendedAldo’s two alerts to Harris’s seemingly narcotics-free truck: According to Wheetley, Harris probably transferred the odor of methamphetamine to the door handle, and Aldo responded to that “residual odor.” Id., at 80.

The trial court concluded that Wheetley had probablecause to search Harris’s truck and so denied the motion to suppress. Harris then entered a no-contest plea whilereserving the right to appeal the trial court’s ruling. An intermediate state court summarily affirmed. See 989 So. 2d 1214, 1215 (2008) (per curiam).

The Florida Supreme Court reversed, holding that Wheetley lacked probable cause to search Harris’s vehicleunder the Fourth Amendment. “[W]hen a dog alerts,” thecourt wrote, “the fact that the dog has been trained andcertified is simply not enough to establish probable cause.” 71 So. 3d, at 767. To demonstrate a dog’s reliability, theState needed to produce a wider array of evidence:

“[T]he State must present . . . the dog’s training andcertification records, an explanation of the meaning ofthe particular training and certification, field perfor mance records (including any unverified alerts), and evidence concerning the experience and training of theofficer handling the dog, as well as any other objectiveevidence known to the officer about the dog’s reliabil ity.” Id., at 775.

The court particularly stressed the need for “evidence ofthe dog’s performance history,” including records showing“how often the dog has alerted in the field without illegal contraband having been found.” Id., at 769. That data, the court stated, could help to expose such problems as a handler’s tendency (conscious or not) to “cue [a] dog toalert” and “a dog’s inability to distinguish between resid- ual odors and actual drugs.” Id., at 769, 774. Accordingly,an officer like Wheetley who did not keep full records ofhis dog’s field performance could never have the requisite cause to think “that the dog is a reliable indicator of drugs.” Id., at 773.

Judge Canady dissented, maintaining that the major- ity’s “elaborate and inflexible evidentiary requirements” went beyond the demands of probable cause. Id., at 775. He would have affirmed the trial court’s ruling on thestrength of Aldo’s training history and Harris’s “fail[ure] to present any evidence challenging” it. Id., at 776.

We granted certiorari, 566 U. S. ___ (2012), and now reverse.


A police officer has probable cause to conduct a searchwhen “the facts available to [him] would ‘warrant a [per son] of reasonable caution in the belief ’” that contraband or evidence of a crime is present. Texas v. Brown, 460 U. S. 730, 742 (1983) (plurality opinion) (quoting Carroll v. United States, 267 U. S. 132, 162 (1925)); see Safford Unified School Dist. #1 v. Redding, 557 U. S. 364, 370– 371 (2009). The test for probable cause is not reducible to “precise definition or quantification.” Maryland v. Pringle, 540 U. S. 366, 371 (2003). “Finely tuned standards suchas proof beyond a reasonable doubt or by a preponderanceof the evidence . . . have no place in the [probable-cause] decision.” Gates, 462 U. S., at 235. All we have requiredis the kind of “fair probability” on which “reasonable and prudent [people,] not legal technicians, act.” Id., at 238, 231 (internal quotation marks omitted).

In evaluating whether the State has met this practicaland common-sensical standard, we have consistently looked to the totality of the circumstances. See, e.g., Prin gle, 540 U. S., at 371; Gates, 462 U. S., at 232; Brinegar v. United States, 338 U. S. 160, 176 (1949). We have rejected rigid rules, bright-line tests, and mechanistic inquiries in favor of a more flexible, all-things-considered approach. In Gates, for example, we abandoned our old test for as sessing the reliability of informants’ tips because it haddevolved into a “complex superstructure of evidentiaryand analytical rules,” any one of which, if not complied with, would derail a finding of probable cause. 462 U. S., at 235. We lamented the development of a list of “inflexi ble, independent requirements applicable in every case.” Id., at 230, n. 6. Probable cause, we emphasized, is “afluid concept—turning on the assessment of probabilitiesin particular factual contexts—not readily, or even use- fully, reduced to a neat set of legal rules.” Id., at 232.

The Florida Supreme Court flouted this established approach to determining probable cause. To assess the reliability of a drug-detection dog, the court created a strict evidentiary checklist, whose every item the Statemust tick off.1 Most prominently, an alert cannot estab lish probable cause under the Florida court’s decisionunless the State introduces comprehensive documentationof the dog’s prior “hits” and “misses” in the field. (Onewonders how the court would apply its test to a rookiedog.) No matter how much other proof the State offers of the dog’s reliability, the absent field performance recordswill preclude a finding of probable cause. That is the antithesis of a totality-of-the-circumstances analysis. It is, indeed, the very thing we criticized in Gates when we overhauled our method for assessing the trustworthinessof an informant’s tip. A gap as to any one matter, weexplained, should not sink the State’s case; rather, that“deficiency . . . may be compensated for, in determiningthe overall reliability of a tip, by a strong showing as to . . . other indicia of reliability.” Id., at 233. So too here, a finding of a drug-detection dog’s reliability cannot dependon the State’s satisfaction of multiple, independent eviden tiary requirements. No more for dogs than for human informants is such an inflexible checklist the way to prove reliability, and thus establish probable cause.

Making matters worse, the decision below treats recordsof a dog’s field performance as the gold standard in evi ——————

1By the time of oral argument in this case, even Harris declined to defend the idea that the Fourth Amendment compels the State to produce each item of evidence the Florida Supreme Court enumerated.See Tr. of Oral Arg. 29–30 (“I don’t believe the Constitution requires [that list]”). Harris instead argued that the court’s decision, although“look[ing] rather didactic,” in fact did not impose any such requirement. Id., at 29; see id., at 31 (“[I]t’s not a specific recipe that can’t be de-viated from”). But in reading the decision below as establishing a man datory checklist, we do no more than take the court at its (oft-repeated)word. See, e.g., 71 So. 3d 756, 758, 759, 771, 775 (Fla. 2011) (holdingthat the State “must” present the itemized evidence).

dence, when in most cases they have relatively limitedimport. Errors may abound in such records. If a dogon patrol fails to alert to a car containing drugs, the mis take usually will go undetected because the officer will not initiate a search. Field data thus may not capture a dog’s false negatives. Conversely (and more relevant here), if the dog alerts to a car in which the officer finds no narcot ics, the dog may not have made a mistake at all. The dogmay have detected substances that were too well hidden orpresent in quantities too small for the officer to locate. Or the dog may have smelled the residual odor of drugs pre viously in the vehicle or on the driver’s person.2 Field data thus may markedly overstate a dog’s real false positives. By contrast, those inaccuracies—in either direction—do not taint records of a dog’s performance in standard train ing and certification settings. There, the designers of anassessment know where drugs are hidden and where they are not—and so where a dog should alert and where he should not. The better measure of a dog’s reliability thus comes away from the field, in controlled testingenvironments.3


2See U. S. Dept. of Army, Military Working Dog Program 30 (Pam phlet 190–12, 1993) (“The odor of a substance may be present in enoughconcentration to cause the dog to respond even after the substance has been removed. Therefore, when a detector dog responds and no drugor explosive is found, do not assume the dog has made an error”); S. Bryson, Police Dog Tactics 257 (2d ed. 2000) (“Four skiers toke up inthe parking lot before going up the mountain. Five minutes later a narcotic detector dog alerts to the car. There is no dope inside. How ever, the dog has performed correctly”). The Florida Supreme Court treated a dog’s response to residual odor as an error, referring to the “inability to distinguish between [such] odors and actual drugs” as a“facto[r] that call[s] into question Aldo’s reliability.” 71 So. 3d, at 773– 774; see supra, at 4. But that statement reflects a misunderstanding.A detection dog recognizes an odor, not a drug, and should alert when ever the scent is present, even if the substance is gone (just as a policeofficer’s much inferior nose detects the odor of marijuana for some timeafter a joint has been smoked). In the usual case, the mere chance that the substance might no longer be at the location does not matter; a well-trained dog’s alert establishes a fair probability—all that is re quired for probable cause—that either drugs or evidence of a drugcrime (like the precursor chemicals in Harris’s truck) will be found.



For that reason, evidence of a dog’s satisfactory perfor mance in a certification or training program can itself provide sufficient reason to trust his alert. If a bona fide organization has certified a dog after testing his reliabilityin a controlled setting, a court can presume (subject to any conflicting evidence offered) that the dog’s alert provides probable cause to search. The same is true, even in the absence of formal certification, if the dog has recently and successfully completed a training program that evaluatedhis proficiency in locating drugs. After all, law enforce ment units have their own strong incentive to use effective training and certification programs, because only accuratedrug-detection dogs enable officers to locate contraband without incurring unnecessary risks or wasting limited time and resources.

A defendant, however, must have an opportunity tochallenge such evidence of a dog’s reliability, whether bycross-examining the testifying officer or by introducing his own fact or expert witnesses. The defendant, for example,may contest the adequacy of a certification or training program, perhaps asserting that its standards are too lax or its methods faulty. So too, the defendant may examinehow the dog (or handler) performed in the assessmentsmade in those settings. Indeed, evidence of the dog’s (orhandler’s) history in the field, although susceptible to the kind of misinterpretation we have discussed, may some times be relevant, as the Solicitor General acknowledged

—————— 3See K. Furton, J. Greb, & H. Holness, Florida Int’l Univ., The Scien tific Working Group on Dog and Orthogonal Detector Guidelines 1, 61–62, 66 (2010) (recommending as a “best practice” that a dog’s reliabilityshould be assessed based on “the results of certification and proficiencyassessments,” because in those “procedure[s] you should know whether you have a false positive,” unlike in “most operational situations”).

Opinion of the Court

at oral argument. See Tr. of Oral Arg. 23–24 (“[T]hedefendant can ask the handler, if the handler is on the stand, about field performance, and then the court can give that answer whatever weight is appropriate”). And even assuming a dog is generally reliable, circumstancessurrounding a particular alert may undermine the case for probable cause—if, say, the officer cued the dog (con sciously or not), or if the team was working under un- familiar conditions.

In short, a probable-cause hearing focusing on a dog’salert should proceed much like any other. The court should allow the parties to make their best case, con sistent with the usual rules of criminal procedure. And the court should then evaluate the proffered evidence todecide what all the circumstances demonstrate. If the State has produced proof from controlled settings that a dog performs reliably in detecting drugs, and the defend ant has not contested that showing, then the court shouldfind probable cause. If, in contrast, the defendant has challenged the State’s case (by disputing the reliability of the dog overall or of a particular alert), then the court should weigh the competing evidence. In all events, the court should not prescribe, as the Florida Supreme Courtdid, an inflexible set of evidentiary requirements. The question—similar to every inquiry into probable cause—is whether all the facts surrounding a dog’s alert, viewed through the lens of common sense, would make a reason- ably prudent person think that a search would reveal con- traband or evidence of a crime. A sniff is up to snuff when it meets that test.


And here, Aldo’s did. The record in this case amply supported the trial court’s determination that Aldo’s alert gave Wheetley probable cause to search Harris’s truck.The State, as earlier described, introduced substantial


evidence of Aldo’s training and his proficiency in finding drugs. See supra, at 2–3. The State showed that two years before alerting to Harris’s truck, Aldo had success fully completed a 120-hour program in narcotics detection, and separately obtained a certification from an independ ent company. And although the certification expired aftera year, the Sheriff ’s Office required continuing training for Aldo and Wheetley. The two satisfied the require ments of another, 40-hour training program one year prior to the search at issue. And Wheetley worked with Aldofor four hours each week on exercises designed to keeptheir skills sharp. Wheetley testified, and written recordsconfirmed, that in those settings Aldo always performed at the highest level.

Harris, as also noted above, declined to challenge in the trial court any aspect of Aldo’s training. See supra, at 3. To be sure, Harris’s briefs in this Court raise questions about that training’s adequacy—for example, whether the programs simulated sufficiently diverse environments andwhether they used enough blind testing (in which thehandler does not know the location of drugs and so cannot cue the dog). See Brief for Respondent 57–58. Similarly,Harris here queries just how well Aldo performed in con trolled testing. See id., at 58. But Harris never voiced those doubts in the trial court, and cannot do so for the first time here. See, e.g., Rugendorf v. United States, 376 U. S. 528, 534 (1964). As the case came to the trial court,Aldo had successfully completed two recent drug-detectioncourses and maintained his proficiency through weeklytraining exercises. Viewed alone, that training record—with or without the prior certification—sufficed to estab lish Aldo’s reliability. See supra, at 8–9.

And Harris’s cross-examination of Wheetley, which focused on Aldo’s field performance, failed to rebut the State’s case. Harris principally contended in the trialcourt that because Wheetley did not find any of the substances Aldo was trained to detect, Aldo’s two alerts must have been false. See Brief for Respondent 1; App. 77–80.But we have already described the hazards of inferring too much from the failure of a dog’s alert to lead to drugs, see supra, at 7; and here we doubt that Harris’s logic doesjustice to Aldo’s skills. Harris cooked and used metham phetamine on a regular basis; so as Wheetley later sur mised, Aldo likely responded to odors that Harris had transferred to the driver’s-side door handle of his truck. See supra, at 3. A well-trained drug-detection dog should alert to such odors; his response to them might appeara mistake, but in fact is not. See n. 2, supra. And still more fundamentally, we do not evaluate probable cause inhindsight, based on what a search does or does not turn up. See United States v. Di Re, 332 U. S. 581, 595 (1948).For the reasons already stated, Wheetley had good causeto view Aldo as a reliable detector of drugs. And no specialcircumstance here gave Wheetley reason to discount Aldo’susual dependability or distrust his response to Harris’s truck.

Because training records established Aldo’s reliability in detecting drugs and Harris failed to undermine that show ing, we agree with the trial court that Wheetley had prob able cause to search Harris’s truck. We accordingly reverse the judgment of the Florida Supreme Court.

It is so ordered.