THE STATE OF ILLINOIS, PETITIONER V. LANCE GATES, ET UX. No. 81-430 In the Supreme Court of the United States October Term, 1981 On Writ of Certiorari to the Supreme Court of Illinois Brief for the United States as Amicus Curiae TABLE OF CONTENTS Interest of the United States Statement Summary of argument Argument A. The informant's tip, together with police corroboration of details of the tip, established probable cause 1. Probable cause may be established by corroboration of "innocent details" of a tip that do not necessarily indicate criminal activity 2. Corroboration of an informant's tip may establish probable cause even if the tip standing alone fails to satisfy the "basis of knowledge prong" of the Aguilar test B. The Illinois Supreme Court failed adequately to consider the fact that the search was conducted pursuant to a warrant Conclusion QUESTION PRESENTED Whether the Illinois Supreme Court correctly ordered the Suppression of evidence seized pursuant to a warrant search on the ground that the supporting affidavit, consisting of information provided by an anonymous informant and the results of police surveillance substantially corroborating most of the information provided by the informant, did not establish probable cause. INTEREST OF THE UNITED STATES This case presents an important question concerning the standards for determining whether probable cause exists when an anonymous informant's tip is substantially corroborated by police investigation. Although this is a state prosecution, this question also arises frequently in federal cases and has received inconsistent treatment in the federal courts of appeals. Accordingly, the United States has a direct and significant interest in the standard applicable to such cases. STATEMENT 1. On May 3, 1978, the police department of Bloomingdale, Illinois, received an anonymous handwritten letter alleging that the respondents, who are husband and wife, were engaged in drug trafficking. The letter asserted that respondent Susan Gates would be driving to Florida on May 3 and that respondent Lance Gates would be driving the car back to Illinois a few days later loaded with drugs. The full text of the letter read as follows (Pet. App. 1a, 1b-2b): This letter is to inform you that you have a couple in your town who strictly make their living on selling drugs. They are Sue and Lance Gates, they live on Greenway, off Bloomingdale Rd. in the condominiums. Most of their buys are done in Florida. Sue his wife drives their car to Florida where she leaves it to be loaded up with drugs, when Lance flys (sic) down and drives it back. Sue flys (sic) back after she drops the car off in Florida. May 3 she is driving down there again and Lance will be flying down in a few days to drive it back. At the time Lance drives the car back he has the trunk loaded with over $100,000.00 in drugs. Presently they have over $100,000.00 worth of drugs in their basement. They brag about the fact they never have to work, and make their entire living on pushers. I guarentee (sic) if you watch them carefully you will make a big catch. They are friends with some big drug dealers, who visit their house often. Lance & Sue Gates Greenway in Condominiums The chief of police gave the letter to Detective Charles Mader, and he proceeded to investigate the allegations contained in it. Detective Mader contacted the office of the Illinois Secretary of State to determine whether that office had any drivers' license record showing an address for respondent Lance Gates in Bloomingdale. That office responded that a Lance B. Gates had been issued an Illinois drivers license that listed his address as 209 D. Dartmouth Drive, Bloomingdale, Illinois. The Secretary of State's office also furnished a physical description of Gates (Pet. App. 2a, 2b, 10b). Detective Mader then contacted a reliable confidential informant who told him, on the basis of certain financial records available to the informant, that Lance B. Gates currently resided at 198 B. Greenway Drive in Bloomingdale. /1/ The informant added that Gates previously had lived at 209 D. Dartmouth Drive, Bloomingdale (id. at 2a, 2b-3b, 10b). Also on May 3, 1978, Detective Mader contacted Chicago Police Officer Ott at O'Hare Airport. After checking the flight information available to him, Officer Ott informed Mader that "L. Gates" had made a reservation on Eastern Airlines flight number 245, scheduled to depart O'Hare at 4:15 p.m. on May 5, 1978. The final destination of the flight was West Palm Beach, Florida. Officer Ott also told Detective Mader that the call-back telephone number left with the reservation was 980-8427, which Detective Mader was able to confirm as the unlisted number of Lance Gates on Greenway Drive (Pet. App. 2a, 3b, 11b). On May 5, 1978, Agent William Morely of the Drug Enforcement Administration informed Detective Mader that, pursuant to Detective Mader's instructions, he had observed all passengers boarding Eastern Airlines flight 245 and that an individual using the name Lance Gates and matching the physical description furnished by the Secretary of State had boarded the airplane (id. at 2a, 3b, 11b). The following day, Agent Morely again contacted Detective Mader and told him that DEA agents had just completed a surveillance of Lance Gates in West Palm Beach. The agents observed Gates arrive at the West Palm Beach airport on May 5 and remain there for an hour before taking a taxi to the West Palm Beach Holiday Inn. Lance Gates then entered a room registered to Susan Gates. At 7 a.m. on May 6, 1978, Lance Gates and a woman left the Holiday Inn room, entered a Mercury automobile bearing Illinois license number RS 8437, and headed north on the interstate highway on the route that would be used to go to the Chicago area (Pet. App. 2a, 3b-4b, 11b-12b). Agent Morely also told Detective Mader that a check of Illinois records had revealed that the observed license plate number was registered to Lance B. Gates for a different car, a 1975 Hornet station wagon, and that the driving time from West Palm Beach to Bloomingdale was approximately 21-23 hours (id. at 2a, 4b, 12b). That same day, Detective Mader applied for a search warrant from an associate judge of the circuit court of DuPage County, Illinois. The warrant application was supported by an affidavit signed by Detective Mader reciting all the facts set forth above, as well as copies of the anonymous letter, the envelope in which it was mailed, and the response of the Illinois Secretary of State. /2/ The judge issued a search warrant authorizing the police to search respondents, their condominium apartment in Bloomingdale, and the Mercury automobile (Pet. App. 2a-3a, 4b). On May 7, 1978, at 5:15 a.m., respondents arrived at their residence in Bloomingdale. They were served with the search warrant by waiting Bloomingdale police officers. A search of the trunk of the Mercury revealed several large bundles of marijuana weighing a total of approximately 350 pounds. A subsequent search of respondents' residence uncovered more marijuana, weapons, ammunition, drug paraphernalia, and several scales used for weighing drugs. The police also ascertained that respondents had cocaine in their possession. Both respondents were indicted on state marijuana possession charges and respondent Lance Gates was indicted separately for possession of an unlicensed firearm (Pet. App. 3a). 2. Prior to trial, respondents filed a motion to quash the search warrant and to suppress all evidence obtained as a result of the searches, arguing that Detective Mader's affidavit did not set forth sufficient facts to support the associate judge's finding of probable cause to issue the warrant. The trial court, the circuit court of DuPage County, ordered the evidence suppressed (Pet. App. 3a). The State appealed, and the Appellate Court of Illinois, Second District, affirmed the trial court's suppression order (Pet. App. 1b-9b). The appellate court stated that this Court's decision in Aguilar v. Texas, 378 U.S. 108 (1964), established a two-pronged test for determining whether an affidavit that relies on an informant's testimony supplies probable cause: (1) the "basis of knowledge" prong requires the magistrate to assess the informant's own basis for the accusation of criminal activity; (2) the "veracity" prong requires the magistrate to assess the affiant's basis for concluding that the informant's tip is trustworthy (Pet. App. 5b-6b). The appellate court pointed out that the informant's letter did not state the basis for his knowledge (id. at 6b). Relying on Stanley v. State, 19 Md. App. 507, 313 A.2d 847 (1974), the court then held that no degree of police corroboration of details of the tip could satisfy the "basis of knowledge" prong by showing that the informant "obtained his information in a reliable way" (Pet. App. 7b-8b). Accordingly, the court concluded that the affidavit did not satisfy the first prong of the Aguilar test (id. at 8b). A divided Supreme Court of Illinois affirmed (Pet. App. 1a-18a). The majority noted the appellate court's ruling that police corroboration of a significant part of the informant's tip could never satisfy a defect in the "basis of knowledge" prong of Aguilar (id. at 11a-12a). However, the majority found it unnecessary to reach this question because it found that "the corroborative evidence here was only of clearly innocent activity" and thus could satisfy "neither the 'basis of knowledge' nor the 'veracity' prong of Aguilar" (id. at 12a). Justices Moran and Underwood dissented (Pet. App. 12a-18a). Noting that the facts in this case closely resembled those in Draper v. United States, 358 U.S. 307 (1959), where this Court found that an informant's tip together with police corroboration of innocent details of that tip established probable cause, the dissenters stated that here the specific, detailed information in the letter combined with the police corroboration of much of that information was enough to satisfy both prongs of the Aguilar test. SUMMARY OF ARGUMENT A. Although the informant's tip in this case, standing alone, did not meet the two-pronged test of Aguilar v. Texas, 378 U.S. 108 (1964), when considered in conjunction with the corroborative information obtained by police surveillance it established probable cause for the issuance of the search warrant. The Illinois Supreme Court erroneously found that the corroboration was insufficient to support a finding of probable cause because only "innocent activity" was observed. Because the probable cause standard requires only a probability of criminal activity, however, it is manifest that the fact that observed activity is consistent with innocence does not negate a finding of probable cause. Nor is it necessary that the particular information in the tip that is corroborated by police observation meet the probable cause standard standing alone. Such a rule would completely ignore the existence of the tip, but this Court has made clear that a tip that fails to meet the Aguilar standard is still a proper ingredient in the probable cause determination if combined with police corroboration. Spinelli v. United States, 393 U.S. 410, 415 (1969). The approach of the Illinois Supreme Court is flatly inconsistent with this Court's decision in Draper v. United States, 358 U.S. 307 (1959). In Draper, the Court found that police corroboration of details supplied by an informant, in conjunction with the informant's accusation that the suspect was carrying narcotics, established probable cause even though the conduct observed by the police was completely innocuous -- the suspect was observed alighting from a train dressed exactly as described by the informant. In this respect, this case is actually much stronger than Draper, because here the information corroborated by police surveillance was suspicious in itself. Lance Gates was observed flying down to Florida one afternoon and driving back to Chicago the next morning, as predicted by the informant. While this unusual behavior did not necessarily indicate criminal activity, it did fit a pattern for drug distribution activities and thus further increased the likelihood that the informant's accusation was true. This corroboration, together with the tip, plainly was sufficient to support a finding of probable cause. The Illinois Appellate Court recognized that the corroboration here was relevant to the probable cause determination, but it held that corroboration could be used to remedy a defect only in the "veracity prong" of the Aguilar test; because it believed that the tip here failed to satisfy the "basis of knowledge prong" of Aguilar, the court held that corroboration of the tip could not possibly establish probable cause. This holding is erroneous on two counts. First, it is established that the "basis of knowledge prong" can be satisfied by "self-verifying detail." See Spinelli v. United States, supra, 393 U.S. at 416. Here, the detailed description given by the informant of respondents' modus operandi indicated that he gained his information in a reliable manner, and thus the "basis of knowledge prong" was satisfied even without corroboration. More important, there is no basis for the court's distinction between the two prongs of the Aguilar test with respect to the use of corroboration. Draper, which involved an informant known to be reliable, demonstrates that corroboration can remedy a defect in the "basis of knowledge prong," and other decisions of this Court confirm that view. Indeed, the rule advanced by the Illinois Appellate Court is quite perverse in that it permits the "basis of knowledge prong" to be satisfied by uncorroborated detail but not by independent corroboration of details supplied by the informant. The ultimate question for the magistrate is always whether a reasonable person would conclude from the facts presented in the affidavit that probable cause exists. When the affidavit includes hearsay information, the magistrate must determine whether there is a "substantial basis for crediting the hearsay." Jones v. United States, 362 U.S. 257, 269 (1960). Aguilar establishes a specific framework for this determination when the affidavit is based solely on hearsay. Outside of that particular context, however -- for example when independent investigation partially corroborates the tip -- the Aguilar test should not be applied rigidly. Corroboration may well establish the reliability of the tip far better than could a statement of the informant's "basis of knowledge." Indeed, in the case of anonymous tips, where the informant cannot be questioned about the source of his information, corroboration is the only means available to establish probable cause. The proper test for assessing the corroboration of a tip is that set forth in Spinelli v. United States, supra, 393 U.S. at 415: Is the tip together with the corroboration as trustworthy as a tip that meets the Aguilar test standing alone? This test applies whether or not the tip standing alone satisfies the "basis of knowledge prong." On the facts here, the extensive corroboration of the informant's description of respondents' modus operandi meets this test. B. The courts below also erred in failing to consider the fact that the search here was conducted pursuant to a warrant. A judicial officer's determination of probable cause in issuing a warrant is entitled to "great deference." Spinelli v. United States, supra, 393 U.S. at 419. Thus, cases where the question of probable cause is a marginal one should be resolved by upholding the magistrate's finding. United States v. Ventresca, 380 U.S. 102, 109 (1965). Moreover, suppression in a case like this one does not advance the purposes of the exclusionary rule. The police here acted in exemplary fashion at all times and conducted the search in good faith in reliance on the warrant issued by a neutral judicial officer. Obviously, in the absence of any official misconduct, suppression here can have no beneficial deterrent effect. If anything, it could have the deleterious effect of tending to discourage police officers from submitting their evidence to a judicial officer before acting. ARGUMENT A. The Informant's Tip, Together With Police Corroboration Of Details Of The Tip, Established Probable Cause In Aguilar v. Texas, 378 U.S. 108 (1964), this Court established a two-pronged test for determining whether an affidavit based solely on an informant's tip provides probable cause to believe that an individual is engaged in criminal activity so as to support the issuance of a search warrant. The Court held that, in assessing an affidavit based on hearsay information, "the magistrate must be informed of some of the underlying circumstances from which the informant concluded that the narcotics were where he claimed they were, and some of the underlying circumstances from which the officer concluded that the informant * * * was 'credible' or his information 'reliable.'" 378 U.S. at 114. The two aspects of this test are often referred to as the "basis of knowledge prong" and the "veracity prong" respectively. See Pet. App. 5a-6a. Even though an informant's tip, standing alone, does not satisfy the Aguilar test, it does not necessarily follow that an affidavit relying in significant part on that tip cannot establish probable cause. "(W)here the initial impetus for an arrest is an informer's tip, information gathered by the arresting officers can be used to sustain a finding of probable cause for an arrest that could not adequately be supported by the tip alone" (Whiteley v. Warden, 401 U.S. 560, 567 (1971), and the same is true, of course, of a finding of probable cause for the issuance of a search warrant. Thus, in Draper v. United States, 358 U.S. 307 (1959), an informant told the police that Draper would arrive from Chicago carrying narcotics on either of two days, and he gave a detailed description of Draper, the clothes he would be wearing, and the briefcase he would be carrying. When the police observed Draper alight from a train on the second day wearing clothes and carrying a briefcase that matched the information in the tip, the Court held that there existed probable cause to arrest. 358 U.S. at 313-314. In Spinelli V. United States, 393 U.S. 410 (1969), the Court considered whether a tip that satisfied neither prong of the Aguilar test constituted probable cause when considered in conjunction with certain information obtained by the police. In finding that probable cause was lacking, the Court identified the relevant inquiry in such a case (393 U.S. at 415): "(The magistrate) must ask: Can it fairly be said that the tip, even when certain parts of it have been corroborated by independent sources, is as trustworthy as a tip which would pass Aguilar's tests without independent corroboration?" 1. Probable Cause May be Established by Corroboration of "Innocent Details" of a Tip That Do Not Necessarily Indicate Criminal Activity The Illinois Supreme Court found here that the extensive police corroboration of the information contained in the informant's letter could not remedy the failure of the tip to meet the Aguilar test. The court stated that the police corroborated only respondents' address, Lance Gates's flight to Florida, his entry into a hotel room registered to his wife, and his leaving the hotel the next morning by car. Because this was all "innocent activity," the court held that it was "insufficient to support a finding of probable cause" (Pet. App. 12a). This conclusion is an erroneous statement of the law that rests on a misperception of the probable cause standard and the weight that partial corroboration can lend to an informant's accusation of criminal activity. It is axiomatic that the probable cause standard is satisfied by evidence that falls short of establishing an individual's culpability. "Only a probability of criminal activity is necessary for there to be probable cause." United States v. Gimelstob, 475 F.2d 157, 160 (3d Cir.), cert. denied, 414 U.S. 828 (1973). See generally Adams v. Williams, 407 U.S. 143, 148-149 (1972); Beck v. Ohio, 379 U.S. 89, 91 (1964); Brinegar v. United States, 338 U.S. 160, 175-176 (1949). Thus, the fact that the police investigation corroborated only innocent activity, i.e., activity that was not inherently criminal, is not inconsistent with the existence of probable cause. It is possible that the Illinois Supreme Court did not intend to suggest that activity consistent with innocence could never support a finding of probable cause; rather, its statement about innocent activity could be read to state only that the activity observed by the police here was probably innocent and hence the affidavit did not establish probable cause. That statement, however, would also be erroneous. The fact that the information observed by the police, standing alone, does not amount to probable cause cannot automatically mean that the affidavit as a whole necessarily falls short of establishing probable cause. If it did, the result would be that the receipt of the tip is a factor that is to be completely ignored. But this Court has specifically rejected the notion that an informant's tip that fails to meet the Aguilar test plays no part in the probable cause determination. As explained above (pages 11-12, supra), Spinelli v. United States, supra, 393 U.S. at 415, holds that a tip combined with the results of police investigation that corroborates information contained in the tip can establish probable cause if the tip, coupled with the corroboration, is as trustworthy as an uncorroborated tip that meets the Aguilar test. The error of the Illinois Supreme Court's approach is demonstrated by this Court's decision in Draper v. United States, supra. In Draper, an informant stated that Draper would be carrying narcotics when he arrived on one of two trains. The police observed Draper alight from one of the specified trains, and the informant's description of Draper and his clothes matched perfectly. In the absence of the tip, however, the police observed no more than a man getting off a train carrying a briefcase -- more innocent behavior could hardly be imagined. Nonetheless, this Court held that the tip, in conjunction with the police corroboration of innocent details of the tip, established probable cause, and, indeed, the Court has subsequently reaffirmed that the corroboration in Draper made it "perfectly clear that probable cause had been established." Spinelli v. United States, supra, 393 U.S. at 418. In short, the fact that the particular activities observed by the police do not alone establish probable cause or are not themselves inherently suspicious does not mean that those observations may not establish probable cause in conjunction with an informant's tip that they corroborate. /3/ Finally, the Illinois Supreme Court's characterization of respondents' conduct here as "clearly innocent" is questionable. In fact, the behavior observed by the police was quite suspicious, and, as such, it lends further weight to the informant's tip than would corroboration of ordinary details of everyday life. See 1 W. LaFave, Search and Seizure Section 3.3, at 557 (1978). See, e.g., Ker v. California, 374 U.S. 23, 35-36 (1963). Lance Gates flew down from Chicago to Florida late one afternoon, went to a hotel, and then arose early the next morning and commenced a 22-hour drive back to Chicago in a car with his Illinois license plate. While this unusual behavior did not necessarily indicate criminal activity, it did fit a pattern for drug distribution activities and thus was inherently suspicious in a way that the observed behavior in Draper was not. /4/ As one commentator has explained, "(f)or corroboration to be incriminating rather than innocent, it is not necessary that the events observed by the police supply probable cause by themselves or that they point unequivocally in the direction of guilt. It is sufficient that they are 'unusual and inviting explanation,' though 'as consistent with innocent as with criminal activity.'" 1 W. LaFave, supra, at 557, quoting State v. Alaimo, 34 N.Y.2d 187, 189, 313 N.E.2d 55, 56 (1974). The police observation of respondents' suspicious activities, which matched the informant's description of their modus operandi for acquiring illicit drugs, surely was sufficient to support a finding of probable cause. /5/ 2. Corroboration of an Informant's Tip May Establish Probable Cause Even if the Tip Standing Alone Fails to Satisfy the "Basis of Knowledge Prong" of the Aguilar Test The Illinois Appellate Court recognized that police corroboration of the information in an informant's tip, even "innocent details," can play a role in the probable cause determination. It held, however, that corroboration is relevant only where the tip fails to satisfy the "veracity prong" of the Aguilar test; if the tip alone does not satisfy the "basis of knowledge prong," the court held, no amount of corroboration by the police can remedy that defect and thus supply probable cause (Pet. App. 7b-8b). This distinction is based on a misunderstanding of Aguilar, and it has no basis in the Fourth Amendment. a. At the outset, we note that the conclusion of both courts below (Pet. App. 10a-11a, 6b-7b) that the tip in this case standing alone does not satisfy the "basis of knowledge prong" is open to serious question. Both courts recognized the so-called "self-verifying detail" rule of Spinelli, i.e., that this prong of the Aguilar test may be satisfied in the absence of a statement explaining the manner in which the informant obtained his information if the tip "describe(s) the accused's criminal activity in sufficient detail that the magistrate may know that he is relying on something more substantial than a casual rumor circulating in the underworld or an accusation based merely on an individual's general reputation." 393 U.S. at 416. The courts below, however, found the detail here insufficient. The detail supplied by the informant here was considerably greater than that involved in the accusation in Spinelli, which this Court held lacked sufficient detail. The informant's letter gave a detailed description of the modus operandi of the smuggling operation, explaining that Susan Gates would drive the car to Florida, where it would be loaded with drugs, and then Lance Gates would fly to Florida to drive the car back to Illinois. The tip also gave the exact date of the respondents' next trip to Florida. It also described the street location of respondent's residence and stated the amount of drugs presently stored there and the amount ordinarily brought back on one of the Florida trips. Finally, the letter noted that respondents "brag about the fact they never have to work" and that major drug dealers often visit their home, suggesting that the informant had some personal contact with respondents. This wealth of detail is certainly sufficient to dispel the possibility that the informant's accusation was based merely on "a casual rumor" or respondents' "general reputation." Indeed, while the informant here did not give a description of respondents or their clothing, his description of the criminal enterprise was substantially more detailed than in Draper, which this Court has identified as a "suitable benchmark" for assessing the self-verifying detail of an informant's statement. Spinelli v. United States, supra, 393 U.S. at 416-417. b. Assuming that the detail here falls short of satisfying the "basis of knowledge prong," however, the holding of the Illinois Appellate Court (Pet. App. 7b-8b) and the suggestion of the Illinois Supreme Court (id. at 11a-12a) to the effect that corroboration of the tip cannot possibly establish probable cause are erroneous. Nothing in the decisions of this Court, which consistently contemplate the possibility of establishing probable cause by means of police investigation of tips that do not meet the Aguilar test, suggests that corroboration can cure a defect in the "veracity prong" but not the "basis of knowledge prong." Indeed, these decisions uniformly reject such a distinction. /6/ The leading decision on this point is Draper, where the informant had an established track record for reliability. See 358 U.S. at 309. Hence, the "veracity prong" clearly was satisfied, and the police corroboration on which the Court relied to establish probable cause was necessary only because the tip failed to satisfy the "basis of knowledge prong." Similarly, in both Adams v. Williams, supra, and Ker v. California, supra, the Court relied on police corroboration of a tip by a reliable informant (407 U.S. at 146-147; 374 U.S. at 35). Moreover, a Spinelli, though it ultimately considered the corroboration there insufficient, the Court's extensive discussion of the weight to be given to police corroboration indicates its view that probable cause could have been established in that case by adequate corroboration even though the tip plainly failed to reveal the informant's basis of knowledge (393 U.S. at 416). /7/ Thus, it is clear that this Court consistently has contemplated that corroboration can remedy a failure of a tip to meet the "basis of knowledge prong." While the courts below relied on dictum in one case from an intermediate state court (Stanley v. State, 19 Md. App. 507, 313 A.2d 847 (1974)), the federal courts of appeals have almost uniformly drawn no distinction that would bar the use of corroboration to establish probable cause where a tip fails to meet the Aguilar "basis of knowledge prong." See, e.g., United States v. Haynie, 637 F.2d 227, 232-233 (4th Cir. 1980); United States v. Sanders, 631 F.2d 1309, 1312-1313 (8th Cir. 1980); United States v. Baker, 577 F.2d 1147, 1150 (4th Cir.), cert. denied, 439 U.S. 850 (1978); United States v. Edmond, 548 F.2d 1256 (6th Cir.), cert. denied, 433 U.S. 912 (1977); United States v. Tuley, 546 F.2d 1264, 1268 (5th Cir.), cert. denied, 434 U.S. 837 (1977); United States v. Myers, 538 F.2d 424, 426 (D.C. Cir. 1976), cert. denied, 430 U.S. 908 (1977); United States v. Horton, 488 F.2d 374, 378-379 (5th Cir. 1973), cert. denied, 416 U.S. 993 (1974); United States v. Caniesco, 470 F.2d 1224, 1229-1231 (2d Cir. 1972); but see United States v. Bush, 647 F.2d 357, 365 (3d Cir. 1981). The rule suggested by the courts below is perverse in that it permits the "basis of knowledge prong" to be satisfied by uncorroborated details supplied by the informant under the "self-verifying detail" rule (see Spinelli v. United States, supra, 393 U.S. at 416-417), but not by independent corroboration of details supplied by the informant. If the mere recitation of details by an informant supports the inference that he obtained his information in a reliable manner, then surely the corroboration by independent investigation of details supplied by the informant, even if fewer details are involved, also can support an inference that the informant obtained his knowledge in a reliable manner. /8/ The error of the courts below stems from an unduly narrow focus on the specifics of the Aguilar test, although that decision is merely an application of broad Fourth Amendment principles. In determining whether to issue a search warrant, the question before the magistrate is always whether a reasonable person would conclude from the facts presented in the affidavit that probable cause exists. This decision is complicated somewhat when the affidavit relies on hearsay information provided by an informant. In those circumstances, this Court has said that the magistrate must determine whether there is a "substantial basis for crediting the hearsay." Jones v. United States, 362 U.S. 257, 269 (1960). See also United States v. Ventresca, 380 U.S. 102, 108 (1965). Aguilar does not depart from this approach. See United States v. Harris, 403 U.S. 573, 581 (1971) (opinion of Burger, C.J.). Rather, Aguilar establishes two critical factors -- the basis of the informant's knowledge and his veracity -- to be considered in the particular context where the affidavit is based solely on an informant's tip. Outside of that context, however, such as when independent investigation reveals additional information or corroborates the tip, the specific formulation of the two-pronged test need not be followed rigidly. Rather, the magistrate must examine all the facts to see whether probable cause exists, though this judgment is still informed by a comparison with the Aguilar test. See Spinelli v. United States, supra, 393 U.S. at 415. This is necessarily so because the nature of the corroboration frequently establishes the reliability of the tip far better than could a statement of the informant's "basis of knowledge." Probable cause may exist even if the "basis of knowledge prong" is not strictly satisfied. /9/ Strict insistence on the satisfaction of the "basis of knowledge prong" by a partially corroborated tip is particularly inappropriate where, as here, the tip is anonymous. When the accusation of criminal activity is made by a police officer (see Nathanson v. United States, 290 U.S. 41 (1933)), or even an informant known to the police, it makes good sense for the magistrate to insist on being told the basis for the accusation -- a simple question asked of the accusing police officer or informant should reveal the source. Cf. Aguilar v. Texas, supra, 378 U.S. at 114 n.4. When the informant is anonymous, however, the police cannot question him about his basis of knowledge. If such an anonymous tip is uncorroborated, Aguilar makes clear that the tip does not establish probable cause. But there is no reason to deny police the opportunity to investigate the tip and establish probable cause through partial corroboration; yet a general rule barring corroboration of a tip that fails to satisfy the "basis of knowledge prong" would do just that. The result of such a rule would be to limit severely the utility to law enforcement personnel of anonymous tips, which are vitally important in detecting organized crime and narcotics violations. See United States v. White, 648 F.2d 29, 43-44 (D.C. Cir. 1981), cert. denied, No. 80-6704 (Oct. 13, 1981). The proper test for assessing the corroboration of a tip is that set forth in Spinelli: Is the tip together with the corroboration as trustworthy as a tip that meets the Aguilar test standing alone? On the facts of this case, the answer clearly is yes. The tip predicted that respondents would undertake a narcotics smuggling trip in a particular manner on a particular date. Law enforcement agents observed respondent Lance Gates make the trip in the manner and at the time predicted by the informant, and, moreover, the unusual nature of the trip suggested no likely purpose for the trip other than the criminal purpose identified by the informant. Surely this degree of corroboration provides a stronger basis for believing the informant's accusation of criminal activity than would a statement in the anonymous letter that the information was based on the informant's personal knowledge or some additional detail about Lance Gates' clothes and physical appearance -- either of which would have enabled the tip to meet the "basis of knowledge prong" without any corroboration. In short, the police observations that corroborated the informant's tip about respondents' modus operandi and the date of their next trip to Florida gave the circuit judge who issued the warrant reason to find that "the suspicions engendered by the informant's report (had) ripen(ed) into a judgment that a crime was probably being committed." Spinelli v. United States, supra, 393 U.S. at 418. B. The Illinois Supreme Court Failed Adequately To Consider The Fact That The Search Was Conducted Pursuant To A Warrant Even assuming that the question whether the affidavit here failed to establish probable cause is closer than we have argued, and that a magistrate could properly have refused to issue a warrant on this showing, the Illinois courts erred in failing to accord any deference to the circuit judge's determination that a warrant should issue. It cannot seriously be disputed that the detailed tip and corroboration here created a degree of suspicion that, at the very least, was close to probable cause. This Court stated in United States v. Ventresca, supra, 380 U.S. at 109: "Although in a particular case it may not be easy to determine when an affidavit demonstrates the existence of probable cause, the resolution of doubtful or marginal cases in this area should be largely determined by the preference to be accorded to warrants." As a result, this Court consistently has recognized that the "determination of probable cause (by a magistrate issuing a warrant) should be paid great deference by reviewing courts." Spinelli v. United States, supra, 393 U.S. at 419. See also United States v. Watson, 423 U.S. 411, 423 (1976); Aguilar v. Texas, supra, 378 U.S. at 111; Jones v. United States, supra, 362 U.S. at 270-271. The courts below paid no heed to this principle. The result is that, even though the police here faithfully submitted their information for consideration by a neutral judicial officer and acted in full compliance with the Constitution, indispensable evidence of a serious crime has been suppressed because a reviewing court disagreed with the issuing judicial officer on the nuances of what constitutes probable cause. That result is inconsistent with "a system of justice responsive both to the needs of individual liberty and to the rights of the community." United States v. Ventresca, supra, 380 U.S. at 112. Indeed, it is questionable whether the purposes of the exclusionary rule are served at all by suppression of evidence seized by police action in good faith pursuant to a validity obtained warrant, even if the magistrate's determination of probable cause is later determined to have been erroneous. /10/ This Court has established that "the application of the (exclusionary) rule (is) restricted to those areas where its remedial objectives are thought most efficaciously served." United States v. Calandra, 414 U.S. 338, 348 (1974). In the Fourth Amendment context, the principal purpose of the exclusionary rule is to deter official misconduct. See, e.g., Stone v. Powell, 428 U.S. 465, 486 (1976); United States v. Janis, 428 U.S. 433, 459 n.35 (1976); United States v. Peltier, 422 U.S. 531, 536-539 (1975). Here, there was no misconduct by the police, who acted in good faith at all times, and therefore suppression can have no beneficial deterrent effect. See, e.g., United States v. Peltier, supra, 422 U.S. at 542; Michigan v. Tucker, 417 U.S. 433, 447 (1974); United States v. Williams, 622 F.2d 830, 840-846 (5th Cir. 1980), cert. denied, 449 U.S. 1127 (1981). /11/ Suppression is particularly inappropriate here because of the meticulous care taken by the police to ensure that their conduct at all times comported with constitutional requirements. First, rather than taking precipitous action based on the tip, the police independently investigated the allegations in the tip and sought to corroborate them through surveillance of Lance Gates. When their surveillance confirmed the accuracy of much of the information provided in the tip, the police did not act on their own initiative, but instead sought a warrant from a neutral judicial officer. /12/ Moreover, they provided the judicial officer with every bit of information they possessed that would assist him in making a reasoned, independent decision, including copies of the informant's letter and the report from the Illinois Secretary of State (see Pet. App. 4b, 10b). And they executed the warrant properly and in the good faith belief that it was valid. In these circumstances, it would serve no Fourth Amendment policy to suppress the seized evidence; indeed, suppression could have the deleterious effect of tending to discourage police officers from submitting their evidence to a judicial officer before acting. See United States v. Ventresca, supra, 380 U.S. at 108. CONCLUSION The judgment of the Illinois Supreme Court should be reversed. Respectfully submitted. REX E. LEE Solicitor General D. LOWELL JENSEN Assistant Attorney General ALAN I. HOROWITZ Assistant to the Solicitor General DAVID B. SMITH Attorney MARCH 1982 /1/ As Detective Mader explained in the search warrant affidavit, he had known the confidential informant for the previous two years, during which time the informant had provided him with information several dozen times, resulting in seven arrests and seven convictions (Pet. App. 2b-3b, 10b). /2/ The affidavit is reprinted at Pet. App. 10b-12b. /3/ This Court has pointed out that conduct that appears wholly innocent on its face may indicate criminal activity to a trained and experienced law enforcement officer. United States v. Mendenhall, 446 U.S. 544, 563 (1980) (Powell, J., concurring); Brown V. Texas, 443 U.S. 47, 52 n.2 (1979). By the same token, conduct that appears innocent on its face may indicate criminal activity when considered in conjunction with additional information supplied to the police by an informant. /4/ In particular, law enforcement officers recognize that a short round-trip to an area known to be a source of narcotics, such as Florida, is often an indication of illicit narcotics activity. See, e.g., United States V. Mendenhall, 446 U.S. 544, 562 (1980) (Powell, J., concurring); United States V. Viegas, 639 F.2d 42 (1st Cir.), cert. denied, 451 U.S. 970 (1981); United States V. Price, 599 F.2d 494, 501 & n.9 (2d Cir. 1979). /5/ The court's reliance to the contrary (Pet. App. 12a) on Whiteley V. Warden, supra, is completely misplaced. In Whiteley, the Court simply noted that the additional information in that case, which established no more than that either the informant or the sheriff knew the suspects and the kind of car they drove, did not provide probable cause. Indeed, the Whiteley Court specifically cited Draper as a case where probable cause existed because the additional information obtained by the police corroborated the informant's tip that the suspect was in the process of committing a crime, even though that corroboration was of innocent activity. See 401 U.S. at 567. Just as in Draper, the tip here described the means by which respondents would commit their crime and specified the date on which it would occur, and hence the police observations corroborated the tip that the crime was in progress at the time. /6/ Neither the decisions below nor the other authorities that reject corroboration as a means of satisfying the "basis of knowledge prong" dispute that corroboration can cure a defect in the "veracity prong." In the words of the Maryland decision on which the courts below relied, this is because "(p)resent good performance shows (the informant) to be probably 'credible' just as surely as does past good performance." Stanley V. State, 19 Md. App. 507, 529, 313 A.2d 847, 861 (1974). For the reasons stated earlier, we believe that the police corroboration here satisfied the "veracity prong" even though the anonymous informant obviously was not previously known to be credible. /7/ Indeed, even in Aguilar itself, where the tip obviously met neither prong of the test, the Court indicated that an entirely different case would have been presented if the results of police surveillance of the suspect had been presented to the magistrate. 378 U.S. at 109 n.1. See also Spinelli V. United States, supra, 393 U.S. at 438 (Fortas, J., dissenting). /8/ To be sure, the inference that the informant's accusation of criminal activity has a reliable basis is weak where the corroborated facts are innocuous details that any member of the general public could learn through a chance encounter with the suspect, such as a description of his car. See, e.g., Spinelli V. United States, supra, 393 U.S. at 426-427 (White, J., concurring); United States v. Montgomery, 554 F.2d 754, 758 (5th Cir. 1977). Here, of course, the corroborated facts concerned the manner of carrying out the criminal scheme, and the fact that the informant's information was proven correct was strong evidence that he had access to reliable information not available to the general public. /9/ Indeed, even in the context in which it specifically applies -- an uncorroborated tip -- Aguilar does not necessarily require that the informant's basis of knowledge be revealed. It directs the magistrate to consider the basis of the informant's knowledge, and ordinarily probable cause will not be found where a reliable basis is not shown. However, if an affiant states that he has a tip from an informant who always has refused to reveal his basis of knowledge but whose tips invariably have proven to be accurate on numerous past occasions, it is questionable whether Aguilar would compel a finding of lack of probable cause. /10/ We do not suggest that application of the exclusionary rule is never appropriate when a search has been conducted pursuant to a warrant. Suppression may be justified if the factors relied on by the magistrate "were so lacking in indicia of probable cause as to render official belief in its existence entirely unreasonable" (Brown V. Illinois, 422 U.S. 590, 610-611 (Powell, J., concurring)), or if the warrant was procured in bad faith or on the basis of material misrepresentations (see Franks V. Delaware, 438 U.S. 154 (1978)). /11/ The error perceived by the courts below was made by the judicial officer who issued the warrant. Suppressing evidence on the ground that a warrant should not have been issued because probable cause was lacking is a costly and ineffective way of ensuring that such judicial officers exercise their duties properly. Indeed, it is dubious whether suppression would have any effect at all on the judicial officer's future conduct. While a law enforcement officer will ordinarily be aware of and concerned by a lost prosecution, a judicial officer who issues warrants has no similar personal stake in the outcome of a criminal trial and may even be uninformed of a suppression order. /12/ Because one object of their suspicion was an automobile, the police could have conducted the search of respondents' vehicle without a warrant. See, e.g., Chambers V. Maroney, 399 U.S. 42 (1970). Had they elected to do so, however, the courts would be justified in scrutinizing more closely the adequacy of the information on which they acted.