This case presents a question expressly reserved by the Supreme Court in Franks v. Delaware, 438 U.S. 154, 170 , 98 S.Ct. 2674, 2683 , 57 L.Ed.2d 667 (1978): Under what circumstances is a defendant entitled to disclosure of the identity of a confidential informant in order to challenge the veracity of a search warrant affidavit?

I

In November 1981, a United States Magistrate issued a warrant permitting agents of the Bureau of Alcohol, Tobacco, and Firearms (“ATF”) to search Larry Dean Kiser’s residence in Keyes, California. The warrant authorized seizure of “a .380 caliber, blue steel semi-automatic pistol and evidence of receipt of said firearm.” In his affidavit in support of the warrant, ATF agent Jerry Miller stated he believed Kiser had possession of the described weapon at his home in violation of 18 U.S.C.App. § 1202(a)(1). This was based on information from an informant who had been in Kiser’s residence “within the past 10 days” and had “observed a .380 caliber, blue steel semi-automatic pistol.” The informant had seen the same gun in Kiser’s residence “on several occasions during the past two years.” Miller said he had shown the informant a photocopy of a driver’s license issued to Kiser; the informant identified the person pictured on the license as the owner of the pistol.

Miller’s affidavit also provided information from two local police officers. One, later identified as Officer Plants, advised Miller he had taken the informant to Kiser’s residence, which the informant identified as the place he had seen the pistol during the last two years. Officer Callandrillo advised Miller that he had contacted Kiser at the residence “within the past few months.”

ATF agents executed the warrant and seized methamphetamines, marijuana, drug paraphernalia, and numerous firearms. Kiser was arrested and later indicted for violations of 21 U.S.C. § 841 (a)(1) (possession of controlled substance with intent to distribute) and 18 U.S.C.App. § 1202(a)(1) (possession of firearms by felon).

Kiser sought suppression of all items seized during the search of the residence, challenging both the sufficiency and the veracity of the Miller affidavit. Kiser contended that he had reason to believe that *1270 Miller’s informant was Gene Dwayne Ericson. He asked the court to confirm this belief by inquiring of Miller in camera as to the informant’s identity. If it were revealed that Ericson was the informant, Kiser would request a Franks hearing. He contended that at such a hearing Ericson would provide testimony inconsistent with that attributed to him in the Miller affidavit and would cast serious doubt on the veracity of the affidavit. To support his motion, Kiser filed a lengthy affidavit from Ericson, He also sought to subpoena Ericson and to serve subpoenas duces tecum on officers Miller and Plants, under which they would be required to provide all records and documents relating to the confidential informant.

The district court quashed the subpoenas duces tecum and denied the request for disclosure, concluding that the defendant was only entitled to disclosure where the informant was a percipient witness. The court also refused to conduct an in camera hearing on the informant’s identity. It determined such a hearing would be a way for Kiser to gain information to which he was not entitled. In addition, it found that Ericson’s affidavit was so different from the Miller affidavit that it did not permit the conclusion that Ericson was Miller’s informant.

After a jury trial, Kiser was acquitted of the charges in the indictment but convicted on two counts of the lesser included offense of possession of controlled substances. He was sentenced to two consecutive one-year terms. 1

II

In Franks , the Supreme Court held that the fourth amendment entitled a defendant to challenge the veracity of a search warrant affidavit, and that proof of material perjury or reckless disregard for the truth required exclusion of evidence seized under the warrant. 438 U.S. at 155-56 , 98 S.Ct. at 2676-77 . The Court concluded that a ban on impeachment of the veracity of a warrant affidavit would “denude the probable-cause requirement of all real meaning.” Id. at 168 , 98 S.Ct. at 2682 . As indicated by the Court, post-execution review of the warrant is justified because warrants are issued at an ex parte hearing and often in haste, depriving the magistrate of the opportunity to fully consider the affiant’s veracity, and trial court review is the only efficacious sanction to prevent the challenged police misconduct. Id. at 169-70 , 98 S.Ct. at 2683-84 .

We must reconcile the right announced in Franks with the “informer’s privilege” recognized in Roviaro v. United States, 353 U.S. 53 , 77 S.Ct. 623 , 1 L.Ed.2d 639 (1957), and McCray v. Illinois, 386 U.S. 300 , 87 S.Ct. 1056 , 18 L.Ed.2d 62 (1967). In Roviaro , the Supreme Court acknowledged the public interest in protecting the identity of confidential informants in order to encourage the flow of information necessary in criminal prosecutions. Id. 353 U.S. at 59 , 77 S.Ct. at 627 . The Court expressly limited the scope of this privilege; the interest in anonymity must yield when disclosure “is essential to the fair determination of a cause.” Id. at 61 , 77 S.Ct. at 628 ; see United States v. Whitney, 633 F.2d 902, 911 (9th Cir.1980), cert. denied, 450 U.S. 1004 , 101 S.Ct. 1717 , 68 L.Ed.2d 208 (1981). To determine when disclosure was essential, trial courts were instructed to balance the public interest against the defendant’s right to prepare a defense. Roviaro, 353 U.S. at 62 , 77 S.Ct. at 628 .

The informer in Roviaro was a percipient witness to the crime and was essential to the development of Roviaro’s defense. The Government contends, and the district court implicitly concluded, that the principles supporting Roviaro have no application where the defendant seeks disclosure of the identity of an informant who was not a percipient witness. It argues that the defendant’s interest in a “mere tipster” whose knowledge does not bear on the defendant’s *1271 guilt or innocence is outweighed by the public interest in promoting the flow of confidential information. It emphasizes that “the interests at stake in a suppression hearing are of lesser magnitude than those in the criminal trial itself.” United States v. Raddatz, 447 U.S. 667, 679 , 100 S.Ct. 2406, 2414 , 65 L.Ed.2d 424 (1980).

It is clear, however, that these factors do not preclude disclosure when the informant’s identity is relevant only to the probable cause determination. United States v. Anderson, 509 F.2d 724, 729 (9th Cir.), cert. denied, 420 U.S. 910 , 95 S.Ct. 831 , 42 L.Ed.2d 840 (1975). In McCray v. Illinois, the Court held that the due process clause does not require a fixed rule mandating disclosure at a pretrial hearing. 386 U.S. at 311-13 . However, McCray did not hold that the informer’s privilege was absolute. It implicitly endorsed disclosure where alternate means of assuring the existence of probable cause are not available. Franks, 438 U.S. at 170 , 98 S.Ct. at 2683 ; Anderson, 509 F.2d at 729 .

We conclude, therefore, that the limited right of disclosure announced in Roviaro and McCray is consistent with the challenge to the warrant affidavit permitted under Franks . We hold that a defendant who claims the affidavit misrepresents or invents information supplied by a confidential informant is, in some instances, entitled to a Franks hearing. We further hold, however, that the public interest protected in Roviaro and McCray imposes unique procedural requirements and evidentiary burdens on the defendant who advances such a claim. As stated in Franks , there is a presumption that the officer who relies on an informant reports valid information and relies on his source in good faith. Franks, 438 U.S. at 171 , 98 S.Ct. at 2684 .

To show entitlement to a Franks hearing, the defendant must make specific allegations that indicate the portions of the

warrant claimed to be false. Id.; see West Point-Pepperell, Inc. v. Donovan, 689 F.2d 950, 959-60 (11th Cir.1982). There must be a contention of deliberate falsehood or reckless disregard for the truth. Franks, 438 U.S. at 171 , 98 S.Ct. at 2684 ; see United States v. Davis, 617 F.2d 677, 694 (D.C.Cir. 1979). The allegations must be accompanied by a detailed offer of proof, preferably in the form of affidavits. Franks, 438 U.S. at 171 , 98 S.Ct. at 2684 ; United States v. Chesher, 678 F.2d 1353, 1360 (9th Cir.1982); United States v. Young Buffalo, 591 F.2d 506, 509 (9th Cir.), cert. denied, 441 U.S. 950 , 99 S.Ct. 2178 , 60 L.Ed.2d 1055 (1979). The offer of proof must challenge the veracity of the affiant, not that of his informant. Franks, 438 U.S. at 171 , 98 S.Ct. at 2684 ; see In re Search Warrant Dated July 4, 1977, 667 F.2d 117, 137 (D.C.Cir.1981), cert. denied, 456 U.S. 926 , 102 S.Ct. 1971 , 72 L.Ed.2d 441 (1982); United States v. Schauble, 647 F.2d 113, 117 (10th Cir.1981). Finally, the challenged statements in the affidavit must be necessary to a finding of .probable cause. United States v. Flores, 679 F.2d 173, 176 (9th Cir.1982), cert. denied, - U.S. -, 103 S.Ct. 791 , 74 L.Ed.2d 996 (1983); Chesher, 678 F.2d at 1360 .

A defendant in Kiser’s situation has a difficult evidentiary problem. To make a substantial preliminary showing, he must establish a negative — that the informant does not exist — or uncover the informant’s probable identity and the text of his information, despite considerable Government efforts to protect both. See 2 W. LaFave, Search and Seizure: A Treatise on the Fourth Amendment § 4.4(d) (1978). Kiser’s offer of proof was sufficient to satisfy that burden. Its primary element was the nine-page Ericson affidavit. Because of factual similarities between the Ericson and Miller affidavits, this provided preliminary evidence that Ericson was Miller’s informant. 2 *1272 We disagree with the district court’s conclusion that the two affidavits were too different to permit this inference.

Other sections of the Ericson affidavit contain information materially different from that attributed to the informant by Miller. For example, Ericson stated he told Officer Plants that Kiser had moved out of state two years previously, and that Ericson had not seen him since that time. He stated that he told Officer Plants that he did not know who owned the house or the vehicle parked there. He also stated that he denied knowing Miller, and said he had neither been shown nor identified a driver’s license issued to Kiser.

The Government argues that Ericson’s affidavit was insufficient as a preliminary showing; it relies on our decision in United States v. Kim, 577 F.2d 473 (9th Cir.1978). Kim is inapposite for two reasons. First, the Kim affidavits challenged the informants’ veracity, but not that of the warrant affiant. Id. at 479 . This would not be an adequate preliminary showing under Franks 3 Second, the Kim defendants relied entirely on the informants’ affidavits. Id. at 478 n. 5. In contrast, Kiser’s offer of *1273 proof included evidence in addition to Ericson’s affidavit. He offered the testimony of Frances Ericson and of Philip Oliver, a Federal Public Defenders Office investigator, as to the conditions under which the affidavit was taken and what was said. The record at the time of the Franks motion also included the testimony of Officers Callandrillo and Plants, both of whom Miller quoted in his affidavit. Miller stated that Callandrillo had “personally contacted [Kiser] at his residence for investigative purposes within the past few months.” Callandrillo testified he told Miller he had not seen Kiser since the spring of 1980, which would have been about eighteen months before the date of the warrant, and that he did not enter Kiser’s property at that time, but that as far as Callandrillo knew, Kiser still lived at the residence. When Officer Plants testified, Kiser’s attorney attempted to verify Miller’s account of the trip Plants and the informant made to Kiser’s residence. The court precluded this line of questioning as likely to expose the informant’s identity.

This offer of proof constituted a substantial preliminary showing that Ericson was the informant and that the Miller affidavit misstated important facts. We do not conclude, however, that this showing automatically entitled Kiser to disclosure of the informant’s identity. Instead, we suggest the district court adopt procedures to protect the public interest, the informant, and the defendant.

The first step in this case should be an ex parte, in camera hearing to determine whether Ericson was, in fact, Miller’s informant. Kiser concedes that if the court is satisfied that Ericson was not the informant, that ends the inquiry.

If Kiser has correctly identified the informant, the ex parte, in camera hearing must be extended. Its purpose should be to determine if Kiser is entitled to an open evidentiary hearing on his Franks claim. We have frequently authorized in camera hearings in sensitive situations similar to this. See United States v. Licavoli, 604 F.2d 613, 621 (9th Cir.1979), cert. denied, 446 U.S. 935 , 100 S.Ct. 2151 , 64 L.Ed.2d 787 (1980); United States v. Moore, 522 F.2d 1068, 1072 (9th Cir.1975), cert. denied, 423 U.S. 1049 , 96 S.Ct. 775 , 46 L.Ed.2d 637 (1976); United States v. Tutwiler, 505 F.2d 758, 760 (9th Cir.1974); Durham v. United States, 403 F.2d 190, 196 (9th Cir.1968), vacated on other grounds, 401 U.S. 481 , 91 S.Ct. 858 , 28 L.Ed.2d 200 (1971); see also 1 W. LaFave Search and Seizure: A Treatise on the Fourth Amendment § 3.3(g) (1978). “The in camera procedure provides an equally-acceptable accommodation of the competing interests of the Government and the accused in the situation presented here, wherein the question is whether a law enforcement officer has lied. Through disclosure of the informer’s identity to the trial judge, and such subsequent inquiries by the judge as may be necessary, the Government can be protected from any significant, unnecessary impairment of necessary secrecy, yet the defendant can be saved from what could be serious police misconduct.” Moore, 522 F.2d at 1072-73 .

At the in camera hearing, the trial judge should question Miller, the local police officers quoted in the Miller affidavit, and any other individuals he deems necessary to the determination. 4 We emphasize that the in camera inquiry is not a substitute for an evidentiary hearing. Its purpose is merely to determine if Kiser has made a “threshold substantial showing of falsehood.” Id. at 1073 .

If the trial court finds that such a showing has been made, Kiser is entitled to a Franks hearing. 5 It will then be his burden *1274 to establish by a preponderance of the evidence his allegation that Miller’s affidavit was untrue. Franks, 438 U.S. at 156 , 98 S.Ct. at 2676 . The Government’s contentions that the Ericson affidavit was coerced or is otherwise incredible may be fully explored at that hearing. Because the district court made no findings on these charges, we express no opinion as to their merit.

Kiser also alleges that Miller intentionally or recklessly omitted from his affidavit several material items of information. The effect of misrepresentations and omissions on the existence of probable cause is to be considered cumulatively. United States v. Esparza, 546 F.2d 841, 844 (9th Cir.1976). Therefore, if a Franks hearing is held, the district court should also consider these contentions.

We vacate Kiser’s conviction and remand to the district court for an in camera hearing and, if necessary, a Franks hearing. The in camera hearing should be transcribed and its record sealed. In the event the district court finds Kiser is not entitled to a Franks hearing, or if such a hearing is held and Kiser does not establish' his claim, the court may reinstate the judgment of conviction. See United States v. Davis, 663 F.2d 824, 830-31 (9th Cir.1981).

VACATED and REMANDED.

. The suppression hearing was held before Judge Crocker; the presiding judge at the jury trial was Judge Coyle.

. Agent Miller’s affidavit stated in part:

Gene Dwayne Ericson’s affidavit stated in part:

. We note that Kim predated Franks , and thus did not consider the relationship of Franks, Roviaro, and McCray .

. We reject the Government’s contention that an adequate inquiry is not possible because of Ericson’s death. The issue is not Ericson’s veracity, but Miller’s. See Franks, 438 U.S. at 171 , 98 S.Ct. at 2684 . A preliminary determination on the Miller affidavit can be made by questioning the officers.

. The Government suggests that Kiser’s opportunity to question Miller at the suppression hearing was a satisfactory substitute for a Franks hearing. We disagree. Kiser’s attorney questioned Miller after the district court had denied Kiser’s motions for a Franks hearing and for disclosure, and those rulings neces *1274 sarily circumscribed the line of questioning. The court sustained objections to any questions concerning the informant.