concurring:
This case presents us with three substantive issues: First, whether summary judgment was properly granted in favor of Officers Liggett, Parga, and Barham on the Fullers’ claim that these officers unlawfully arrested them; second, whether summary judgment was properly granted in favor of Officer Barham on the Fullers’ claims that Officer Barham unlawfully subjected them to a visual body cavity search (“strip search”); third, whether summary judgment was properly granted in favor of the City of Los Angeles on the Fullers’ claims that they were unlawfully strip searched pursuant to city policy. Although I agree with the majority’s ultimate resolution of each of these issues, I disagree with portions of its analysis. Accordingly, I write separately.
I
The majority correctly concludes that qualified immunity shields officers Liggett, Parga, and Barham from liability for the arrest of the Fullers. However, the majority’s analysis is seriously flawed. In deter*1453mining whether reasonable officers in the arresting officers’ positions could have believed that they had probable cause to execute a warrantless arrest, the majority asks whether the arresting officers fulfilled their “duty to investigate” before arresting the Fullers. In its analysis, the majority subtly promulgates the rigid rule that arresting officers have a “duty to conduct an investigation into the basis of” an eyewitness report before making an arrest that is founded on the report. Ante at 1444. The majority erroneously recognized an independent “duty to investigate” as a vehicle for promulgating police procedures.
It is clearly established that the presence or absence of probable cause is a fact-specific, practical inquiry that turns on the “totality of the circumstances.” Illinois v. Gates, 462 U.S. 213, 238-39, 103 S.Ct. 2317, 2332, 76 L.Ed.2d 527 (1983); United States v. Lindsey, 877 F.2d 777, 781 (9th Cir.1989). “Rigid legal rules are ill-suited to an area of such diversity.” Gates, 462 U.S. at 232, 103 S.Ct. at 2329. It is equally well established that qualified immunity applies if a reasonable police officer could have believed that his or her conduct was lawful, in light of clearly established law and the information the officers possessed. Anderson v. Creighton, 483 U.S. 635, 641, 107 S.Ct. 3034, 3039, 97 L.Ed.2d 523 (1987); Thorsted v. Kelly, 858 F.2d 571, 573 (9th Cir.1988); Merriman v. Walton, 856 F.2d 1333, 1335 (9th Cir.1988), cert. denied, 491 U.S. 905, 109 S.Ct. 3188, 105 L.Ed.2d 696 (1989). Thus, to decide whether the arresting officers have qualified immunity we should consider only whether in the “totality of the circumstances” known to the arresting officers, these officers reasonably could have thought that they possessed probable cause to arrest the Fullers. See Creighton, 483 U.S. at 641, 107 S.Ct. at 3039; Thorsted, 858 F.2d at 573; Merriman, 856 F.2d at 1335.
We have never recognized, as the majority purports to recognize, a “duty to investigate” component of this probable cause inquiry. The majority’s sole support for its “duty to investigate” is Merriman v. Walton, 856 F.2d 1333 (9th Cir.1988), cert. denied, 491 U.S. 905, 109 S.Ct. 3188, 105 L.Ed.2d 696 (1989). However, the majority’s reliance on Merriman is completely misplaced. Indeed, in Merriman we closely analyzed the information known to the arresting officer in order to decide what we considered to be the key question: "Whether a reasonable police officer, knowing what [the arresting officer] knew, could have believed there was probable cause for Merriman’s warrantless arrest_ Probable cause is determined by applying a ‘totality-of-the-circumstances’ analysis” Id. at 1335.1 Given what the officer knew, we held that there was not enough information to support probable cause, and stated that “[a] reasonable police officer would have made further inquiry before effecting a warrantless arrest.” The majority mistakenly relies on this statement because it was nothing more than an offhanded admonishment. Id. Obviously, when the evidence does not support a finding of probable cause, the logical response is to say that the officers should have inquired further. In short, the majority’s view that Merri-man creates an independent “duty to investigate” is baseless, and is inconsistent with both Ninth Circuit and Supreme Court precedent.
Even though the majority erroneously dwells on its “duty to investigate,” the majority correctly concludes that in the instant case the arresting officers are entitled to qualified immunity. In light of the “totality of the circumstances,” which are adequately described in the majority opinion, “a reasonable police officer, knowing what [the arresting officers] knew, could have believed there was probable cause for [the Fullers’] warrantless arrest.” Merriman, 856 F.2d at 1335; see also Creighton, 483 U.S. at 641, 107 S.Ct. at 3039.
II
The second major question before us is whether Officer Barham is entitled to qual*1454ified immunity from the Fullers’ claim that she unlawfully subjected them to a strip search. The majority has correctly described the standards against which evi-dentiary strip searches are measured: such searches must be justified by probable cause, and a warrant must be obtained prior to the search in the absence of exigent circumstances. The majority also correctly concludes that this standard was not clearly established at the time that the instant strip searches took place. Thus, I agree with the majority’s conclusion that Officer Barham is entitled to qualified immunity for the strip searches. See Creighton, 483 U.S. at 641, 107 S.Ct. at 3039; The Presbyterian Church (U.S.A.) v. United States, 870 F.2d 518, 526 (9th Cir.1989); Conner v. City of Santa Ana, 897 F.2d 1487, 1492 (9th Cir.) (holding that the law was clearly established), cert. denied, — U.S. -, 111 S.Ct. 59, 112 L.Ed.2d 34 (1990).
Unfortunately, the majority goes considerably further than is necessary. The majority not only discerns the relevant standard, but the majority goes on to apply this standard to the facts of the instant case. This latter step is simply unnecessary. As the majority itself concludes, the probable cause/warrant standard was not “clearly established” at the time of the searches in issue, and as a result Officer Barham is entitled to immunity. See Creighton, 483 U.S. at 641, 107 S.Ct. at 3039.
Moreover, it is worth stressing that the probable cause/warrant standard that we recognize today operates in a very limited sphere. Officer Barham’s search for the ring is evaluated under the probable cause/warrant standard only because the search cannot be justified by reference to the security needs of a detention facility; the defendants have admitted that there was no reason to suspect that the Fullers were harboring drugs, weapons, or other contraband that would have posed a security threat to the facilities at which the Fullers were detained. If the circumstances surrounding a strip search do justify a reasonable suspicion that a suspect is harboring contraband that will pose a security threat to a detention facility, then the search is constitutionally valid. See Kennedy v. Los Angeles Police Dept., 901 F.2d 702, 712, 715-16 (9th Cir.1990) (holding that strip searches of felony suspects are permissible if justified by a reasonable suspicion that drugs or weapons are being smuggled into a detention facility; no warrant is required); Ward v. County of San Diego, 791 F.2d 1329, 1332-1333 (9th Cir.1986) (holding that prison security related searches of misdemeanor arrestees are justified by reasonable suspicion that the ar-restees have weapons or contraband on their persons), cert. denied sub nom, Duffy v. Ward, 483 U.S. 1020, 107 S.Ct. 3263, 97 L.Ed.2d 762 (1987); Giles v. Ackerman, 746 F.2d 614, 617 (9th Cir.1984) (holding that, in light of the jail’s need for security, strip searches of person arrested for a minor traffic offenses are valid if undertaken on the basis of “reasonable suspicion that the individual arrestee is carrying or concealing contraband”), cert. denied, 471 U.S. 1053, 105 S.Ct. 2114, 85 L.Ed.2d 479 (1985).
Ill
The final issue in this case is whether summary judgment was properly granted in favor of the City of Los Angeles. While I agree with the majority that this case should be remanded in order for Los Ange-les’ liability to be determined at trial, the majority’s analysis is incomplete in one respect and overbroad in another.
A municipality is liable under Section 1983 only if “action pursuant to official municipal policy of some nature caused a constitutional tort.” Monell v. Department of Social Services, 436 U.S. 658, 691, 98 S.Ct. 2018, 2036, 56 L.Ed.2d 611 (1978); see also City of Canton, Ohio v. Harris, 489 U.S. 378, 389, 109 S.Ct. 1197, 1205, 103 L.Ed.2d 412 (1989). Thus, in order for Los Angeles to be liable for the actions of its officers three conditions must be established: First, there must be a constitutionally infirm municipal policy in issue; second, this municipal policy must have been applied to plaintiff; third, application of this policy must have resulted in the deprivation of a constitutional right. See id. Although the majority’s treatment of the *1455first and second Monell conditions is generally adequate, the majority’s casual one-sentence discussion of the third Monell condition is inadequate. We must determine whether the Fullers’ Fourth Amendment interest in freedom from unreasonable searches was violated in this case by the application of the City’s facially invalid strip search policy.
The application of a facially unconstitutional search policy to an individual does not establish a “per se” constitutional violation. See Kennedy, 901 F.2d at 715. For the Constitution forbids only objectively “unreasonable” searches. See U.S. Const, amend. IV; Torres v. Commonwealth of Puerto Rico, 442 U.S. 465, 471, 99 S.Ct. 2425, 2429, 61 L.Ed.2d 1 (1979) (“the grounds for a search must satisfy objective standards”). If in the circumstances of a particular case a search is objectively reasonable, there is no constitutional violation. Thus, in order to decide whether the Fullers were deprived of their right to be free of unreasonable searches, we must determine whether the searches in issue were justified by probable cause, and whether exigent circumstances rendered a warrant unnecessary.2 See Part II, supra.
Probable cause does not require certainty. Rather, “[t]his court must make a ‘practical, common-sense decision’ whether under the ‘totality of the circumstances’ known to [Officer Barham] at the time ... there was a ‘fair probability’ that contraband or evidence of a crime would be found_” Lindsey, 877 F.2d at 780 (quoting Gates, 462 U.S. at 238-39, 103 S.Ct. at 2332 (1983)).
Contrary to the majority’s intimations, there was probable cause to strip search the Fullers. The offense for which the Fullers were arrested was theft of a small but valuable object, a ring. Obviously, a ring may easily be concealed in a body cavity. Officer Barham had received an eyewitness report that the Fullers had taken the ring, and interviews with other witnesses at the scene confirmed this eyewitness report. One of the Fullers could have secreted the ring in a body cavity during the interval between the time they left the jewelry store and the time that they were fingered by the store keeper. During this period the Fullers were unobserved. Or the Fullers might have secreted the ring in a body cavity during the substantial confusion that ensued after the store keeper accused them of stealing it.3 Further, searches in the areas which the Fullers were known to have lingered did not turn up the ring, and these areas were searched before the Fullers were subjected to the strip searches. In these circumstances, there was a “fair probability” that the ring would be found if the Fullers were strip searched.
Still, in order for a warrantless strip search to be valid, the circumstances must establish exigency as well as probable cause. “Exigent circumstances are defined as ‘those circumstances that would cause a reasonable person to believe that entry ... [or other relevant prompt action] was necessary to prevent physical harm to the officers or other persons, the destruction of relevant evidence, the escape of the suspect, or some other consequence improperly frustrating legitimate law enforcement efforts.’ ” Lindsey, 877 F.2d at 780-81 (quoting United States v. McConney, 728 F.2d 1195, 1199 (9th Cir.) (en banc), cert. denied, 469 U.S. 824, 105 S.Ct. 101, 83 L.Ed.2d 46 (1984)). We have recognized that exigent circumstances may be presented based solely on the need to preserve evidence. See United States v. Wulfer-dinger, 782 F.2d 1473, 1475 (9th Cir.1986); *1456United States v. Hicks, 752 F.2d 379, 384 (9th Cir.1985); United States v. Kunkler, 679 F.2d 187, 190 (9th Cir.1982). However, the government has the burden of establishing that the searching officers were confronted with exigent circumstances. Lindsey, 877 F.2d at 781.
In the instant case, the City of Los Ange-les has presented no evidence that it could not monitor the Fullers, who were in custody, or otherwise prevent the Fullers from disposing of the ring. Absent some such presentation, we cannot say that exigent circumstances rendered a warrant unnecessary. See Bouse v. Bussey, 573 F.2d 548, 550 (9th Cir.1977) (holding that exigent circumstances were not presented because there was no danger that the evidence would be destroyed). Cf. United States v. Suarez, 902 F.2d 1466, 1468 (9th Cir.1990) (holding that exigent circumstances were not presented because the government could have monitored the apartment house which contained evidence to prevent the evidence’s destruction). Thus, Officer Bar-ham’s failure to obtain a warrant rendered the strip searches that she conducted on the Fullers constitutionally “unreasonable.” As such, the third Monell condition for municipal liability is met. I therefore agree that we must remand this case to the district court so that a jury may determine whether the unconstitutional strip searches were conducted pursuant to the City’s automatic strip search policy.
Unfortunately, the majority is not content to have the Fullers win on the basis on which they argued their case. The majority states that there is a material issue of fact as to whether: “Officer Barham was acting pursuant to an LAPD policy or custom of conducting visual body cavity inspections in order to detect stolen property without probable cause and/or without a warrant.” The Fullers have never argued that they were searched pursuant to any such municipal policy. And it is well established that a district court will not be reversed on a ground not raised before it. See Image Technical Service, Inc. v. Eastman Kodak, 903 F.2d 612, 615 n. 1 (9th Cir.1990) (holding that plaintiff's failure to raise an issue in opposition to a defendant’s motion for summary judgment waived the issue), cert. granted, — U.S. -, 111 S.Ct. 2823, 115 L.Ed.2d 994 (1991); United States v. Munoz, 746 F.2d 1389, 1390 (9th Cir.1984) (refusing to consider a tort theory not raised below in a contract action). Thus, on remand the Fullers should be limited to arguing, as they have throughout this litigation, that they were strip searched pursuant to the City’s automatic strip search policy.
With these reservations, I concur.
. Merriman had been arrested for kidnapping. The arresting officer knew, inter alia, “that Mer-riman ... was [the alleged victim’s] long-time boyfriend ... [and that] the alleged victim of the kidnapping had returned.” Id. We concluded that “[u]nder these circumstances, there is no probable cause.” Id.
. Although the majority fails to make this inquiry, the majority's views on the matter are clearly indicated by the majority’s conclusion, made in the course of its qualified immunity analysis, that Officer Barham violated the Fullers’ Fourth Amendment rights when she strip searched them.
. The majority asserts that the Fullers had no opportunity to hide the ring in a body cavity after being confronted by the store keeper because "it appears that the Fullers were not out of the sight of other witnesses at any time after Kashanian confronted them_” Ante at 1451. This assertion is misleading. While the Fullers were generally in public areas during this period, they certainly were not under any surveillance.