(Slip Opinion)
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` OCTOBER TERM, 2012
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`Syllabus
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`1
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` NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
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` being done in connection with this case, at the time the opinion is issued.
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` The syllabus constitutes no part of the opinion of the Court but has been
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` prepared by the Reporter of Decisions for the convenience of the reader.
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` See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.
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`SUPREME COURT OF THE UNITED STATES
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` Syllabus
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`FLORIDA v. HARRIS
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`CERTIORARI TO THE SUPREME COURT OF FLORIDA
` 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 to
`conclude 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
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` 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 and
`performance in the field, particularly in the two stops of Harris’s
`truck. The trial court denied the motion to suppress, but the Florida
` Supreme 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 falsely
`
`alerted. If an officer like Wheetley failed to keep such records, he
`could never have probable cause to think the dog a reliable indicator
`of 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
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`search, all that is required is the kind of “fair probability” on which
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` “reasonable and prudent [people] act.” Illinois v. Gates, 462 U. S.
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` 213, 235. To evaluate whether the State has met this practical and
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`FLORIDA v. HARRIS
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`
`Syllabus
`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 by
`
`creating 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 no
`matter 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 the
`evidentiary gold standard when, in fact, such data may not capture a
`dog’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 a
`
`dog’s alert should proceed much like any other, with the court allow-
`
`ing the parties to make their best case and evaluating the totality of
`the 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 the
`
`
`testifying officer or by introducing his own fact or expert witnesses.
`The defendant may contest training or testing standards as flawed or
`too lax, or raise an issue regarding the particular alert. The court
`should then consider all the evidence and apply the usual test for
`probable cause—whether all the facts surrounding the alert, viewed
`through 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 search
`the 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 this
`first time in this Court. Harris principally relied below on Wheetley’s
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`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-
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`Cite as: 568 U. S. ____ (2013)
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`Syllabus
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`3
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`ing. Pp. 9–11.
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`71 So. 3d 756, reversed.
` KAGAN, J., delivered the opinion for a unanimous Court.
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` Cite as: 568 U. S. ____ (2013)
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`Opinion of the Court
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`1
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` NOTICE: This opinion is subject to formal revision before publication in the
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` preliminary print of the United States Reports. Readers are requested to
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` notify the Reporter of Decisions, Supreme Court of the United States, Wash-
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` ington, D. C. 20543, of any typographical or other formal errors, in order
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` that corrections may be made before the preliminary print goes to press.
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`SUPREME COURT OF THE UNITED STATES
`
`_________________
`
` No. 11–817
`_________________
` FLORIDA, PETITIONER v. CLAYTON HARRIS
`
`
`ON WRIT OF CERTIORARI TO THE SUPREME COURT OF
`
`
`FLORIDA
`
`
`[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 stop
`provides probable cause to search a vehicle. The Florida
`Supreme Court held that the State must in every case
`present an exhaustive set of records, including a log of the
`dog’s performance in the field, to establish the dog’s relia-
`bility. See 71 So. 3d 756, 775 (2011). We think that de-
`
`inconsistent with the “flexible, common-sense
`mand
`
`standard” of probable cause. Illinois v. Gates, 462 U. S.
`213, 239 (1983).
`
`
`
`I
`
`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 to
`detect 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,
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`Wheetley saw that Harris was “visibly nervous,” unable to
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`sit still, shaking, and breathing rapidly. Wheetley also
`noticed an open can of beer in the truck’s cup holder. App.
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` FLORIDA v. HARRIS
`
`Opinion of the Court
`62. Wheetley asked Harris for consent to search the truck,
`but Harris refused. At that point, Wheetley retrieved Aldo
`from the patrol car and walked him around Harris’s truck
`for 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. Wheetley
`accordingly arrested Harris, who admitted after proper
`Miranda warnings that he routinely “cooked” metham-
`phetamine at his house and could not go “more than a few
`days 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 on
`this occasion discovered nothing of interest.
`
`Harris moved to suppress the evidence found in his
`truck 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
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` Cite as: 568 U. S. ____ (2013)
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`Opinion of the Court
`specializes in testing and certifying K–9 dogs. Wheetley
`and Aldo teamed up in 2005 and went through another,
`40-hour refresher course in Dothan together. They also
`did four hours of training exercises each week to maintain
`their 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 with
`that 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 to
`contest 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 before
`
`he 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 defended
`Aldo’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 probable
`cause to search Harris’s truck and so denied the motion to
`suppress. Harris then entered a no-contest plea while
`reserving 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
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` FLORIDA v. HARRIS
`
`Opinion of the Court
`Wheetley lacked probable cause to search Harris’s vehicle
`under the Fourth Amendment. “[W]hen a dog alerts,” the
`court wrote, “the fact that the dog has been trained and
`certified is simply not enough to establish probable cause.”
`71 So. 3d, at 767. To demonstrate a dog’s reliability, the
`State needed to produce a wider array of evidence:
`“[T]he State must present . . . the dog’s training and
`certification records, an explanation of the meaning of
`the particular training and certification, field perfor-
`mance records (including any unverified alerts), and
`evidence concerning the experience and training of the
`officer handling the dog, as well as any other objective
`evidence known to the officer about the dog’s reliabil-
`ity.” Id., at 775.
`The court particularly stressed the need for “evidence of
`the 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 to
`alert” 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 of
`his 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 the
`strength 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.
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` Cite as: 568 U. S. ____ (2013)
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`Opinion of the Court
`
` II
`A police officer has probable cause to conduct a search
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`when “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 such
`as proof beyond a reasonable doubt or by a preponderance
`of the evidence . . . have no place in the [probable-cause]
`decision.” Gates, 462 U. S., at 235. All we have required
`is 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 practical
`
`
`and 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 had
`devolved into a “complex superstructure of evidentiary
`and 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 “a
`fluid concept—turning on the assessment of probabilities
`in 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
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`FLORIDA v. HARRIS
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`Opinion of the Court
`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 State
`must tick off.1 Most prominently, an alert cannot estab-
`lish probable cause under the Florida court’s decision
`unless the State introduces comprehensive documentation
`of the dog’s prior “hits” and “misses” in the field.
`(One
`wonders how the court would apply its test to a rookie
`dog.) No matter how much other proof the State offers of
`the dog’s reliability, the absent field performance records
`will 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 trustworthiness
`of an informant’s tip. A gap as to any one matter, we
`explained, should not sink the State’s case; rather, that
`“deficiency . . . may be compensated for, in determining
`the 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 depend
`on 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 records
`of 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
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`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) (holding
`that the State “must” present the itemized evidence).
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`Cite as: 568 U. S. ____ (2013)
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`Opinion of the Court
`dence, when in most cases they have relatively limited
`import. Errors may abound in such records. If a dog
`on 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 dog
`may have detected substances that were too well hidden or
`present 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 an
`assessment know where drugs are hidden and where they
`are not—and so where a dog should alert and where he
`——————
`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 enough
`concentration to cause the dog to respond even after the substance has
`been removed. Therefore, when a detector dog responds and no drug
`or 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 in
`the 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 police
`officer’s much inferior nose detects the odor of marijuana for some time
`after 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 drug
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`crime (like the precursor chemicals in Harris’s truck) will be found.
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`FLORIDA v. HARRIS
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`Opinion of the Court
`should not. The better measure of a dog’s reliability
`thus comes away from the field, in controlled testing
`environments.3
`
`
`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 reliability
`in 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 evaluated
`his proficiency in locating drugs. After all, law enforce-
`ment units have their own strong incentive to use effective
`training and certification programs, because only accurate
`drug-detection dogs enable officers to locate contraband
`without incurring unnecessary risks or wasting limited
`time and resources.
`
`A defendant, however, must have an opportunity to
`challenge such evidence of a dog’s reliability, whether by
`cross-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 examine
`how the dog (or handler) performed in the assessments
`made in those settings. Indeed, evidence of the dog’s (or
`handler’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 reliability
`should be assessed based on “the results of certification and proficiency
`assessments,” because in those “procedure[s] you should know whether
`
`you have a false positive,” unlike in “most operational situations”).
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` Cite as: 568 U. S. ____ (2013)
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`Opinion of the Court
`at oral argument. See Tr. of Oral Arg. 23–24 (“[T]he
`
`defendant 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, circumstances
`
`surrounding 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’s
`
`
`alert 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 to
`decide 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 should
`
`
` find 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 Court
`did, 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.
`
`
`
`
`III
`
`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
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` FLORIDA v. HARRIS
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`Opinion of the Court
`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 after
`a 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 Aldo
`for four hours each week on exercises designed to keep
`their skills sharp. Wheetley testified, and written records
`confirmed, that in those settings Aldo always performed at
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`the highest level.
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`Harris, as also noted above, declined to challenge in the
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`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 and
`whether they used enough blind testing (in which the
`handler 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,
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`Aldo had successfully completed two recent drug-detection
`courses and maintained his proficiency through weekly
`training exercises. Viewed alone, that training record—
`with or without the prior certification—sufficed to estab-
`lish Aldo’s reliability. See supra, at 8–9.
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`And Harris’s cross-examination of Wheetley, which
`focused on Aldo’s field performance, failed to rebut the
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`State’s case. Harris principally contended in the trial
`court that because Wheetley did not find any of the sub-
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`It is so ordered.
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` Cite as: 568 U. S. ____ (2013)
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`Opinion of the Court
`stances Aldo was trained to detect, Aldo’s two alerts must
`have been false. See Brief for Respondent 1; App. 77–80.
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`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 does
`justice to Aldo’s skills. Harris cooked and used metham-
`phetamine on a regular basis; so as Wheetley later sur-
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`mised, Aldo likely responded to odors that Harris had
`transferred to the driver’s-side door handle of his truck.
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`See supra, at 3. A well-trained drug-detection dog should
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`alert to such odors; his response to them might appear
`a mistake, but in fact is not. See n. 2, supra. And still
`more fundamentally, we do not evaluate probable cause in
`hindsight, 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 cause
`to view Aldo as a reliable detector of drugs. And no special
`circumstance here gave Wheetley reason to discount Aldo’s
`usual dependability or distrust his response to Harris’s
`truck.
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`Because training records established Aldo’s reliability in
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`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.