Opinion for the Court filed by Circuit Judge SPOTTSWOOD W. ROBINSON, III.
Opinion concurring in part and concurring in the judgment filed by Circuit Judge STARR.
SPOTTSWOOD W. ROBINSON, III, Circuit Judge:
In this Freedom of Information Act (FOIA)1 case, appellant, Cynthia King, seeks production by the Federal Bureau of Investigation (FBI) of documents relating to her deceased mother-in-law, Carol King, a civil rights attorney and activist about whose career appellant is writing a book.2 The FBI has released many of the documents — most, however, in redacted form.3 The agency contends that its decision to withhold portions of the requested information is authorized by Exemptions 1 and 7 of the Act,4 which respectively except from FOIA’s disclosure mandate, documents classified for national security reasons and certain other material gathered during investigations for law-enforcement purposes. Appellant challenges the applicability of either exemption in the circumstances presented here.5
The District Court denied motions by appellant for summary judgment or in the alternative to compel discovery, rejected appellant’s request for in-camera inspection, and granted the FBI’s motion for summary judgment.6 This appeal ensued.
I
The records whose disclosure is here at issue are part of an FBI surveillance file on Carol King compiled during the 1940’s and 1950’s. She was a prominent civil rights attorney who devoted her practice to defending minorities, aliens, radicals and union members both famous and obscure;7 and a substantial portion of her practice consisted in representation of aliens facing deportation during the McCarthy era.8 The nature of Carol King’s law practice and her political associations aroused suspicions of the FBI. In 1941, the FBI opened [213]*213a surveillance file on her, and subjected her to continuous investigation until her death in 1952.9 The FBI represents that its investigation was devoted exclusively to determining whether Carol King was guilty of political sedition.10 While the eleven-year investigation amassed a file 1,665 pages in length,11 no charge was ever made.
Appellant is a writer by profession who intends to publish a biography on her mother-in-law and longtime friend, Carol King.12 As yet, no significant history of the latter’s career has been published.13 In the course of her research, appellant attempted to obtain information pertaining to Carol King by means of a FOIA request. The FBI eventually responded by releasing to appellant redacted portions of its King investigative file. Ultimately provided were 1,500 pages of the 1,665-page file, and, from most of the 1,500 pages supplied, names and, frequently, substantial passages were deleted.14
Contesting the sufficiency of the FBI’s response to her FOIA request, appellant filed suit in the District Court,15 and moved for a Vaughn index16 detailing the grounds for the FBI’s exemption claims.17 Production of the Vaughn index was ordered.18 Thereafter, the FBI submitted the joint declaration of Special Agents Richard C. Staver and Walter Scheuplein, Jr.,19 and the declaration of John H. Walker of the Immigration and Naturalization Service,20 attesting to the reasons for excising portions of the King file; it then moved for summary judgment.21 Appellant in turn moved for summary judgment, or in the alternative to compel a response to outstanding discovery requests.22
The District Court granted the FBI’s motion for summary judgment.23 It sustained the Exemption 1 contentions, relying on the Staver-Scheuplein declaration, which it found to set forth with “reasonable specificity of detail rather than mere conclusory statements”24 an adequate description of the portions of the King file withheld, as well as the national security considerations advanced in support of the FBI’s refusal to [214]*214disclose.25 Similarly, the District Court deemed the declaration a sufficient foundation for the FBI’s claims under Exemptions 7(C) and 7(D) that information withheld was gathered pursuant to an investigation for law-enforcement purposes and that its release would constitute an unwarranted invasion of personal privacy or compromise assurances of source confidentiality.26
Appellant urges us to hold that the District Court erred in crediting the FBI’s Exemption 1 and 7 arguments, contending that they shield information in contravention of FOIA’s broad disclosure mandate. Specifically, appellant asserts that the Staver-Scheuplein declaration presents only a vague and conclusory description of the material excised pursuant to Exemption 1, wholly inadequate for purposes of ascertaining whether the documents in question have in fact been properly classified, or what harm might result from their production.27 “How,” appellant queries, “can release of ... records of this nature and at this late date possibly damage the national security?”28 Appellant further contends that the Staver-Scheuplein declaration does not make the threshold showing required for resort to Exemption 7: that the documents in question were compiled for bona fide law-enforcement purposes pursuant to an investigation whose relation to the agency’s law-enforcement duties is based on information sufficient to support at least a “ ‘colorable claim’ of its rationality.”29 And, whether or not a law-enforcement purpose originally animated the investigation, appellant insists no considerations of privacy or confidentiality warrant continued withholding of its fruits.30 While we reject appellant’s challenge to the disposition of the Exemption 7 claims in this case, we believe valid objections to the FBI’s showing on the Exemption 1 claims have been raised, and remand in order that the District Court secure a fuller elaboration of the FBI’s basis for asserting them.31
II
Exemption 1 of the Freedom of Information Act protects from disclosure information that is “specifically authorized under criteria established by an Executive order to be kept secret in the interest of national defense or foreign policy and [is] in fact properly classified pursuant to such Executive order.”32 An agency may invoke this exemption only if it complies with classification procedures established by the relevant executive order and withholds only such material as conforms to the order’s substantive criteria for classification.33 Appellant challenges, on substantive and not procedural grounds, the propriety of the classification decisions underlying the FBI’s Exemption 1 claims.34
A.
Both appellant and the FBI believe that the directive pertinent to disposition of the Exemption 1 issues in this case is Executive Order 12065,35 which was in effect when the FBI’s classification determinations were made.36 This order provided that information could be classified only if it concerned:
[215]*215(a) military plans, weapons, or operations;
(b) foreign government information;
(c) intelligence activities, sources or methods;
(d) foreign relations or foreign activities of the United States;
(e) scientific, technological, or economic matters relating to the national security;
(f) United States Government Programs for safeguarding nuclear materials or facilities; or
(g) other categories of information which are related to national security and which require protection against unauthorized disclosure as determined by the President, by a person designated by the President pursuant to Section 1-201, or by an agency head.37
Executive Order 12065 further specified that information concerning any of the enumerated matters was eligible for classification as “confidential,” the lowest security designation, only if its “unauthorized disclosure ... reasonably could be expected to cause at least identifiable damage to the national security.”38 It also established a presumption against classification: “If there is reasonable doubt ... whether the information should be classified at all ... the information should not be classified.”39 Subsequent to the decision to classify the documents involved in this case, and after commencement of this litigation, President Reagan promulgated Executive Order 12356.40 This order retains all categories of classifiable information enumerated in Executive Order 12065,41 but diverges from that order in several other significant respects. The new executive order eliminates the prior order’s presumption against classification42 and modifies the standard for classifying information. While the earlier order prohibited an agency from classifying information unless it could be shown that “unauthorized disclosure reasonably could be expected to cause at least identifiable damage to the national security,”43 the new order seemingly commands classification of all material within certain enumerated categories of sensitive information whose “unauthorized disclosure, either by itself or in the context of other information, reasonably could be expected to cause damage to the national security.”44 While the old executive order in some instances required declassification decisions to be made by weighing the need to protect in[216]*216formation against the public interest in disclosure,45 the new executive order eliminates this balancing provision from the declassification calculus.46 Absent as well from the new order are certain procedures contained in Executive Order 12065 designed to ensure systematic declassification review of older material.47
The parties have conformed their arguments regarding the propriety of the classification decisions in dispute to the terms of Executive Order 12065, under which those decisions were made,48 notwithstanding the fact that Executive Order 12065 is now superseded by Executive Order 12356. Their position finds support in our holding in Lesar v. United States Department of Justice49 that “[o]n review, the court should ... assess the documents according to the terms of the Executive Order under which the agency made its ultimate classification determination.”50 A brief review of the rationale supporting our position in Lesar and its subsequent elaboration should provide a framework for an assessment of the Exemption 1 claims in this case.
Our decision in Lesar to utilize the terms of a superseded order as the basis for review was explicitly bottomed on considerations of efficiency and, properly understood, is limited to the situations in which efficiency can be pursued with due regard for the national security considerations of paramount concern in Exemption 1 cases. As we observed in Lesar, Executive Order 12065 provided that information classified under prior orders should retain its classified status;51 this carry-over provision enabling a reviewing court to analyze a disputed classification decision under the order in effect at the time the decision was made, in lieu of a remand to the agency for a fresh classification at each juncture of the litigation marked by a new executive order.52 “To hold otherwise and require a remand whenever a new Executive Order issued during the pendency of an appeal would not only place a heavy administrative burden on the agencies but would also cause additional delays in the ultimate processing of these types of FOIA requests.” 53
In Afshar v. Department of State,54 we revisited the question from a somewhat different vantage point. We there considered the question, which we had no occasion to address in Lesar, of which executive order an agency should be directed to apply when the case is remanded with instructions to reconsider a faulty classification determination, and from this perspective we discerned limits to the principle announced in Lesar. While an executive order’s carry-over provision might enable review of a classification decision under the terms of the order in force at the time the decision was made, a remand with an instruction to the agency to reconsider the decision under the terms of a then superseded order would impermissibly bind the Government in an area where flexibility [217]*217and responsiveness to changing world circumstances are at a premium.55
Together, then, Lesar and Afskar direct a reviewing court to assess the propriety of a classification decision purportedly supporting an Exemption 1 claim in terms of the executive order in force at the time the agency’s ultimate classification decision is actually made. Only when a reviewing court contemplates remanding the case to the agency to correct a deficiency in its classification determination is it necessary to discriminate between the order governing for purposes of review and any that may have superseded it, to ensure that on remand the agency will comply only with the most current executive assessment of the Nation’s security needs.56 This two-tiered scheme of review harmonizes the interest in speedy disposition of FOIA requests with that of preserving flexibility in national security determinations. For present purposes, it identifies Executive Order 12065, in force at the time the challenged classification decisions were made, as the directive governing review of the Exemption 1 issues raised in this case.
B.
Turning to the general principles affecting this appeal, we begin with a reminder that, as in all FOIA cases, the district courts are to review de novo all exemption claims advanced,57 and that the agency bears the burden of justifying its decision to withhold requested information.58 The agency may meet this burden by filing affidavits describing the material withheld and the manner in which it falls within the exemption claimed;59 and the court owes substantial weight to detailed agency explanations in the national security context.60 However, a district court may award summary judgment to an agency invoking Exemption 1 only if (1) the agency affidavits describe the documents withheld and the justifications for nondisclosure in enough detail and with sufficient specificity to demonstrate that material withheld is logically within the domain of the exemption claimed,61 and (2) the affidavits are neither controverted by contrary record evidence nor impugned by bad faith on the part of the agency.62 On appeal, the [218]*218court is to determine, from inspection of the agency affidavits submitted, whether the agency’s explanation was full and specific enough to afford the FOIA requester a meaningful opportunity to contest, and the district court an adequate foundation to review, the soundness of the withholding. “Once we are satisfied that [the affidavits provided] the trial court ... an adequate basis to decide, we are guided by the ‘clearly erroneous’ standard in evaluating the substance of that decision.”63
The significance of agency affidavits in a FOIA case cannot be underestimated. As, ordinarily, the agency alone possesses knowledge of the precise content of documents withheld,64 the FOIA requester and the court both must rely upon its representations for an understanding of the material sought to be protected. As we observed in Vaughn v. Rosen,65 “[t]his lack of knowledge by the party seeing [sic ] disclosure seriously distorts the traditional adversary nature of our legal system's form of dispute resolution,”66 with the result that “[a]n appellate court, like the trial court, is completely without the controverting illumination that would ordinarily accompany a lower court’s factual determination.” 67 Even should the court undertake in camera inspection of the material — an unwieldy process where hundreds or thousands of pages are in dispute — 68 “[t]he scope of the inquiry will not have been focused by the adverse parties____”69
Affidavits submitted by a governmental agency in justification for its exemption claims must therefore strive to correct, however, imperfectly, the asymmetrical distribution of knowledge that characterizes FOIA litigation. The detailed public index which in Vaughn70 we required of withholding agencies is intended to do just that: “to permit adequate adversary testing of the agency’s claimed right to an exemp[219]*219tion,”71 and enable “the District Court to make a rational decision whether the withheld material must be produced without actually viewing the documents themselves, as well as to produce a record that will render the District Court’s decision capable of meaningful review on appeal.”72 Thus, when an agency seeks to withhold information, it must provide “a relatively detailed justification, specifically identifying the reasons why a particular exemption is relevant and correlating those claims with the particular part of a withheld document to which they apply.”73 Specificity is the defining requirement of the Vaughn index and affidavit;74 affidavits cannot support summary judgment if they are “conclusory, merely reciting statutory standards, or if they are too vague or sweeping.”75 To accept an inadequately supported exemption claim “would constitute an abandonment of the trial court’s obligation under the FOIA to conduct a de novo review.”76
C.
The District Court examined the affidavits submitted by the FBI in the instant case, and concluded that they substantiated its reliance on Exemption l.77 On appeal, then, we are to determine as a threshold matter whether the affidavits in fact provided the District Court with “an adequate basis to decide” the Exemption 1 issues:78 to ascertain whether the material withheld is within the categories of classifiable information enumerated in Executive Order 12065 and, further, whether its unauthorized disclosure reasonably could be expected to cause the requisite amount of damage to the national security.79 We turn to the Vaughn index and the accompanying declaration prepared by Special FBI Agent, Richard C. Staver.80
Staver advised the District Court that “[t]o provide a more workable ‘Vaughn index’ format and thus reduce the burden of analyzing Exemption One claims” he was departing from the practice of preparing typed pages separately describing each withheld document, and was submitting instead copies of the documents released pursuant to appellant’s FOIA demand with each deletion annotated by means of a four-character code referring in turn to an accompanying code-catalogue.81 The copy [220]*220of the redacted documents and the explanatory code-catalogue together comprise the FBI’s Vaughn filing.
In brief, the system works as follows. For every instance in which information was withheld, the documents released have been marked with the four-character code. The first two characters of the code identify the FOIA exemption assertedly authorizing the withholding — for example, (b)(1); the third character identifies the category in Executive Order 12065 under which the material has been classified — such as Section l-301(c) (intelligence activities, sources or methods); and the fourth character refers to a statement in the code-catalogue that is offered as a description of the material withheld, intended to demonstrate that it lies within one or more of the classification categories of Executive Order 12065, and to point to the likely harm to the national security attending its release.82 In sum, the District Court was presented with an intensively redacted and annotated 1500-page reproduction of the requested file, as well as numerous inserts, similarly annotated, representing the remaining 165 pages of the file withheld.83
Staver opines that this new method of presentation represents “a vast improvement over previous formats” and that “the required specificity has been enhanced.”84 We regret to differ. The system Staver has adopted imposes a significant burden upon the reviewing court without commensurate benefit. Staver’s system of annotation neither adequately describes redacted material nor explains, with sufficient specificity to enable meaningful review, how its disclosure would likely impair national security.85
First, as a practical matter we note that neither the declaration preamble nor the catalogue proffered for descriptive purposes corollates discussion of national security concerns to redacted documents.86 Lacking citations within the declaration to point a reader and the court to the documents in question at each stage of the [221]*221declaration’s exposition, the coding system shifts a sizable portion of the agency’s admittedly imposing burden onto the shoulders of the court.87 In order to weigh the declarant’s arguments, or those offered by counsel in briefs, the court must sift through all of the documents — here 1,500 pages — to find those in issue. To proceed under the alternate strategy — reading the redacted documents and following the code annotations back to the catalogue provided — illuminates the fundamental deficiency of the index format the FBI has adopted. Because it is unhelpfully categorical in nature, the coded commentary supplies little information beyond that which can be gleaned from context.
Apparently the FBI is of the opinion that, by submitting to the court a reproduction of the redacted file, it is relieved of the obligation of describing withheld material in detail.88 Utilization of reproductions of material released to supply contextual information about material withheld is clearly permissible, but caution should be exercised in resorting to this method of description. Such a system is only as good as its results, and the vital result must be an adequate representation of context which, when combined with descriptions of deletions, enables de novo review of the propriety of withholding. In the present case, the system is inadequate because we are left with no contextual description for documents or substantial portions of documents withheld in their entirety,89 an impermissible result as long as revelation of the context would not itself harm the national security. Furthermore, a reproduction of the redacted documents can only show the court the context from which an item has been deleted, and context may or may not assist the court in assessing the character of the excised material and the grounds for its deletion.90 Where it does not, the coded commentary to which the system of annotation leads the court is so general in nature as to be of little or no help.
To carry its burden of demonstrating the propriety of the classification decisions supporting its Exemption 1 position, the FBI must describe with reasonable specificity the material withheld, and identify the damage to the national security expected to attend its disclosure.91 The declaration’s far-ranging category definitions for information classifiable under Executive Order 1206592 make clear that the FBI could pro[222]*222vide subcategory descriptions of redacted material in far more detail than it has.93 Staver’s account of consequences likely to follow disclosure of the information in question is similarly deficient, presenting myriad damage possibilities for each category of classifiable information.94 The ac[223]*223count of the “logical nexus between disclosure ... and damage to the national security” supplied for each subcategory of redacted information95 does little to correct this deficiency because it, too, is categorical in nature.96
We emphasize that our dissatisfaction with the FBI’s Exemption 1 showing arises from the character of the Vaughn index tendered. We express no view on the validity of the underlying classification decisions it is intended to justify. Indeed, we are in no position to evaluate those decisions — to ascertain, for example, whether sensitivity of intelligence information withheld has in any respect diminished with the passage of time97 — for the simple reason that we are not furnished with sufficient information to do so in a meaningful fashion. In decoding the redaction annotations, one encounters at every turn general, not particularized, response. And the generality of the declaration’s subcategory description seems to result, not from cautious avoidance of revealing descriptive detail, but rather from the wide-ranging coverage of the subcategory description itself.98 Similarly, every account the declaration offers of consequences of disclosing material withheld assumes the form of a list whose serial alternatives reflect, not predictive uncertainty about such consequences, as much as the broad contours of the categorization scheme employed.99 Clearly, a series of discrete declassification decisions was necessary to prepare the King file for release, but the texture of these deliberations is everywhere effaced by the coding system employed to justify them to the court.
The Vaughn index here submitted is, in a word, inadequate — wholly lacking in that specificity of description we have repeatedly warned is necessary to ensure meaningful review of an agency’s claim to withhold information subject to a FOIA request.100 A withholding agency must describe each document or portion thereof withheld, and for each withholding [224]*224it must discuss the consequences of disclosing the sought-after information. This requirement, if indeed not explicit in Vaughn, is unmistakably implicit in the principles supporting our decision in that case, as our subsequent decisions have made very clear. When, in Vaughn,101 we first insisted that agencies tender an index and affidavits as a precondition to review of exemptions claims, we emphasized the necessity of identifying which exemption was relied upon for each item withheld.102 In Mead Data Central v. United States Department of the Air Force,103 we elaborated on Vaughn’s requirements, explaining that the withholding agency must supply “a relatively detailed justification, specifically identifying the reasons why a particular exemption is relevant and correlating those claims with the particular part of a withheld document to which they apply.” 104 As we subsequently reiterated in Dellums v. Powell,105 Vaughn’s call for specificity imposes on the agency the burden of demonstrating applicability of the exemptions invoked as to each document or segment withheld.106 Elsewhere we have defined the Vaughn index as “consistpng] of one document that adequately describes each withheld record or deletion and sets forth the exemption claimed and why that exemption is relevant.”107 Categorical description of redacted material coupled with categorical indication of anticipated consequences of disclosure is clearly inadequate.108 To support its Exemption 1 claims, the agency affidavits must, for each redacted document or portion thereof, (1) identify the document, by type and location in the body of documents requested; (2) note that Exemption 1 is claimed; (3) describe the document withheld or any redacted portion thereof, disclosing as much information as possible without thwarting the exemption's purpose; (4) explain how this material falls within one or more of the categories of classified information authorized by the governing executive order; and (5) explain how disclosure of the material in question would cause the requisite degree of harm to the national security.
As we noted in Dellums, a system for categorizing Exemption 1 claims may be appropriate, particularly where the documents in question are voluminous and the same exemption applies to a large number of segments.109 The availability of categorization does not, however, supplant the demand for particularity.110 When the above-listed factors are identical for several documents withheld or items redacted, a single representation, accompanied by identifying references to the documents or portions at issue, may suffice. Similarly, a coding system might be employed to indicate applicability of a given response to more than one segment of redacted material, so long as the information supplied remains responsive to each deleted segment without becoming categorial in tenor. As to each item of excised material, the agency, of course, is to provide as much information [225]*225as is consistent with the national security interests Exemption 1 is designed to protect.111
To be avoided at all costs is “an exercise in the jurisprudence of labels ... offerpng] conclusory assertions regarding [documents] that are not susceptible to such simplistic classification.”112 As we warned in Dellums, the goal of descriptive accuracy is not to be sacrificed to the niceties of a particular classification scheme.113 The measure of a Vaughn index is its descriptive accuracy, and we are willing to accept innovations in its form so long, but only so long, as they contribute to that end.
D.
We conclude that the Vaughn index tendered in this case provides an insufficient basis for the de novo review that FOIA mandates for Exemption 1 claims.114 This requires a remand of the case to the District Court for further proceedings. Then, the court may employ any of several measures to acquire enough information to conduct the review requisite.
The District Court may, in its discretion, order production of the excised material or some sample thereof for in camera inspection.115 An opportunity for “first-hand inspection [enables the court to] determine whether the weakness of the affidavits is a result of poor draftsmanship or a flimsy exemption claim,” but “the district court’s inspection prerogative is not a substitute for the government’s burden of proof, and should not be resorted to lightly.”116 Moreover, should the task of in camera examination appear too burdensome, the court may allow appellant to engage in further discovery,117 or order the FBI to supplement its Vaughn filings.118 If so ordered, the FBI must to provide on an item-specific basis the maximum amount of information consistent with protection of the interests of national security119 and the exigencies of forecasting events in this domain.120
Whether the District Court proceeds by ordering supplemental affidavtis or by in camera inspection of documents or samplings, it must ensure that it has an adequate foundation for review of the FBI’s [226]*226withholding claims before giving the agency’s expert opinion on national security matters the substantial weight to which it is entitled.121 At a minimum, the court must secure more information with respect to excisions involving whole documents or substantial parts thereof, where no contextual information is available to supplement and particularize the FBI’s code descriptions.122 Having garnered this additional information on material withheld, the court should then scrutinize afresh the FBI’s assessment of the consequences of disclosure, allowing appropriate latitude for opinion 123 but ensuring that the enumeration of alternate consequences presently characterizing the agency’s submission reflects predictive uncertainty rather than mere categorical response.
In reviewing the FBI’s predictions on disclosure, the court should devote particular attention to the age of the file in this case. It was compiled between 1941 and 1952; all documents it contains are now at least 35 years old. Executive Order 12065 directs declassification “as early as national security considerations permit,”124 and identifies “the occurrence of a declassification event” or “loss of the information’s sensitivity with the passage of time” as circumstances sufficient to warrant dissolution of a prior classification determination.125 The order’s declassification policy is buttressed by a scheme of mandatory declassification review, concerned especially with material classified in excess of twenty years.126 In light of this policy, the District Court clearly erred in simply deferring to the FBI’s judgment that the sensitivity of the information withheld had not diminished with age,127 particularly since the agency’s only commentary remotely responsive to this concern was its averment that declassification decisions were made in procedural conformity with Executive Order 12065’s directives on prolonged classification.128 An assurance of procedural compliance does not, by itself, afford an adequate foundation for de novo review of the substantive propriety of the withholdings in question;129 in the present case, it raises as many question as it answers. To cite but one example, the Staver-Scheuplein declaration avers that classification was conducted in accordance with FBI implementing regulations, providing in part that category l-301(c) information on intelligence activities, sources and methods presumptively requires classification for a period extending up to twenty years.130 The [227]*227FBI has nevertheless withheld whole documents and passages on the theory that they contain information capable of identifying an intelligence source, leaving us with no contextual information on their general contents and no hint as to why classification of the material was extended decades beyond the period the agency’s own regulations presumptively deem necessary.131 Before a court can accord the deference due the FBI’s considerable expertise on this question, the agency must impart a fair understanding of its reasoning on an item-specific basis.132 In light of [228]*228its claimed reliance on a codified policy respecting declassification of older documents, the FBI is under a particular obligation to account for its apparently continuing decision to prolong classification of those documents whose age exceeds the periods deemed presumptively appropriate for classification by its own regulations.133 On the basis of that showing134 the court will then, and only then, be in position to determine whether, in light of the facts arrayed before it, the Exemption 1 claims can be sustained.135
Ill
Exemption 7 of the Freedom of Information Act, in its provisions pertinent here, excuses from disclosure
records or information compiled for law enforcement purposes, but only to the extent that the production of such law enforcement records or information ... (C) could reasonably be expected to constitute an unwarranted invasion of personal privacy, [or] (D) could reasonably be expected to disclose the identity of a confidential source, including a State, local, or foreign agency or authority or any private institution which furnished information on a confidential basis, and, in the case of a record or information compiled by criminal law enforcement authority in the course of a criminal investigation or by an agency conducting a lawful national security intelligence investigation, information furnished by a confidential source____136
[229]*229To justify a withholding under Exemption 7, an agency must demonstrate, as a threshold matter, that the information it seeks to shield has been “ ‘compiled for law enforcement purposes’ ”137 and, further, that production would have one of the undesirable effects enumerated by the exemption.138
In this circuit, as we have recently observed, “FBI records are not law enforcement records [under FOIA] simply by virtue of the function that the FBI serves.”139 Rather, our decision in Pratt v. Webster140 supplies a two-prong test for determining whether a law-enforcement agency invoking Exemption 7 has made even the threshold showing requisite.141 Pratt requires, first, that the agency “identify a particular individual or a particular incident as the object of its investigation” and specify “ ‘the connection between that individual or incident and a possible security risk or violation of federal law.’ ” 142 The agency must then demonstrate that this relationship is “based on information sufficient to support at least a ‘colorable claim’ of the connection’s rationality.”143 This inquiry, while “necessarily deferential,”
is not vacuous. In order to pass the FOIA Exemption 7 threshold, ... an agency must establish that its investigatory activities are realistically based on a legitimate concern that federal laws have been or may be violated or that national security may be breached. Either of these concerns must have some plausible [230]*230basis and have a rational connection to the object of the agency’s investigation.144
Thus, Pratt in no wise requires a court to sanction agency claims that are pretextual or otherwise strain credulity.145 As we have explained, the threshold showing required by Pratt is an “objective” one, and “suffices to establish the exemption only if it is unrefuted by persuasive evidence that in fact another, nonqualifying reason prompted the investigation,” as “for example [where an investigation is conducted] for purposes of harassment.”146
In the present case, the FBI supplied the following description of the investigation for which the sought-after documents were compiled:
Carol King is the subject of FBIHQ “main” file 100-49864, which is comprised of 1,665 pages. This file is an Internal Security investigative file compiled for law enforcement purposes pursuant to Title 18, U.S.C., Section 2383 (Rebellion or Insurrection), formerly codified as Title 18, U.S.C., Section 4 (1940 ed.), originally enacted as Act of March 4, 1909, ch. 31, Section 4, 35 Stat. 1088; Title 18, U.S.C., Section 2384 (Seditious Conspiracy), formerly codified as Title 18, U.S.C., Section 5 (1940 ed.), originally enacted as Act of March 4,1909, ch. 321, Section 6, 35 Stat. 1089; Title 18 U.S.C., Section 2385 (Overthrow of the Government), formerly codified as Title 18, U.S.C., Sections 10, 11 and 13 (1940 ed.), originally enacted as the Alien Registration Act of 1940, ch. 439, Title I, Sections 2, 3 and 5, 54 Stat. 670, 671. This investigation was opened in 1941 and closed in 1952 after the death of Carol King.147
This account clearly identifies Carol King as the target of the investigation but, to specify the “connection between [her] and a possible security risk or violation of federal law,”148 it simply recites the criminal statutes pursuant to which the investigation was undertaken, presumably indicating that somewhere within the parameters of those general provisions were criminal acts that the FBI suspected her of committing. The FBI, however, contended before the District Court that it had adequate grounds to investigate Carol King in that “Mrs. King was in close association with individuals and organizations that were of investigative interest to the FBI,”149 asserting that the redacted files released to appellant, together with appellant’s own submissions, provided sufficient evidence of such associations to support its claim of law-enforcement purpose.150
Appellant has endeavored to controvert the FBI’s claim on two grounds. First, appellant supplied a series of affidavits attesting to Carol King’s character and beliefs, which were intended to demonstrate that “Carol King did not engage in any of the activities proscribed by the three statutes and that at no time did there exist any ground upon which the FBI could reasonably have suspected that she might have engaged in such activities.”151 Second, appellant launched a broader attack on the propriety of the FBI’s investigation, inti[231]*231mating that the inquiry was calculated to impair Carol King’s efficacy in defending clients whose deportation the Government sought. Surveillance of Carol King, appellant speculates, may have been calculated to secure informational advantage in the litigation of individual cases,152 and to harass and intimidate Carol King in her work as defense counsel generally.153
On cross-motions for summary judgment, the District Court held that the FBI had satisfied Pratt’s threshold showing of law-enforcement purpose.154 Upon inspection, we find this ruling supported by the record. Pratt counsels against “second-guessing” a law-enforcement agency’s showing of investigatory purpose if there is a plausible basis for the undertaking.155 Heeding this admonition, the District Court could properly have concluded that the evidence on Carol King’s character did not, by itself, impugn the plausibility of an investigation premised on the character of her associations. While a factual dispute foreclosing summary judgment would have developed had appellant appropriately buttressed her allegation that a strategem of harassment motivated the investigation, that charge remained wholly devoid of support in the record. In making out a case of pretext, the burden of rebutting an agency showing of law-enforcement purpose rests on the FOIA plaintiff.156 Yet, so far as we can determine, appellant proffered no evidence to support her claim that the investigation of Carol King was undertaken for impermissible reasons.157 Without such ev[232]*232idence, the District Court properly ruled, on the cross-motion for summary judgment, that the record presented no factual issue respecting a law-enforcement purpose stemming from the association that Carol King maintained. We therefore turn to examine the Exemption 7 claims asserted here.
The FBI withheld portions of the King file on the ground that they are protected from disclosure by Exemption 7(C) and (D).158 The material retained was indexed by use of a code catalogue similar to that employed by the FBI in its effort to vindicate its withholding under Exemption 1. Notwithstanding the deficiencies of this descriptive format in the Exemption 1 context,159 we find that it supplies the information requisite for de novo review of the Exemption 7 claims. The latter exemption, in relevant part, concerns issues of privacy and confidentiality arising from the involvement of discrete classes of persons in law-enforcement investigations. The indexing system in question classifies and describes the interests of such persons with sufficient specificity to convey an adequate understanding of the character of the material withheld as well as the justification advanced for withholding.160
Exemption 7(C) immunizes from disclosure records incorporating information gathered for law-enforcement purposes to the extent that its release would “constitute an unwarranted invasion of personal [233]*233privacy.”161 Appellant contends that the FBI improperly invoked the exemption to withhold information that might serve to identify third parties mentioned in the FBI investigative file, third parties identified as subjects of or suspects in the FBI investigative file, and third parties who provided information to law-enforcement officials.162
As the District Court correctly recognized, all three of these classes of persons have a cognizable interest in the privacy of their involvement in a law-enforcement investigation.163 We have admonished repeatedly “that disclosing the identity of targets of law-enforcement investigations can subject those identified to embarassment and potentially more serious reputational harm,”164 and that “[ojther persons involved in the investiation — witnesses, informants, and investigating agents— also have a substantial interest in seeing that their participation remains secret.”165 Third parties discussed in investigatory files may have a similarly strong interest in non-disclosure.166
Having perceived the privacy interests implicated by the King file, the District Court properly undertook to weigh those interests against the public interest in dissemination of file material.167 Though we believe that the court underrated the public interest considerations favoring disclosure, we find correct its ultimate conclusion that the privacy interests here asserted outweigh such public benefit as might attend release of the file information in dispute.
In conducting a de novo review of Exemption 7(C) claims, the district court must "balane[e] the privacy interest^] at stake against the public interest in disclosure.” 168 And the court must remain mindful that while, “[a]s to other exemptions, ‘Congress has struck the balance and the duty of the court is limited to finding whether the material is within the defined category’ ...[,] Exemption 7(C)’s balance is not similarly ‘tilted emphatically in favor of disclosure.’ ”169
Starting from the general premise that “it ‘is difficult, if not impossible, to anticipate all respects in which disclosure might damage reputations or lead to personal embarrassment and discomfort,’ ”170 [234]*234the District Court observed that the “ ‘McCarthy era’ character of this investigation” strengthened the privacy interests militating against release.171 “ ‘A moment’s reflection upon recent political history and the excesses of the internal security investigations of the 1950’s,' ” the court said, “ ‘should be sufficient to signal caution in dealing with unverified derogatory material within the files of an intelligence gathering agency of government.’ ”172 Noting further that public perception of persons thought to have engaged in “subversive” activities, as well as those thought to have associated with such persons, was subject to unpredictable swings, the court rejected appellant’s argument that the passage of time diminished the privacy interests at stake.173 We, in turn, find no basis sufficient to warrant an overturning of the court’s judgment in this regard. Given the varying roles of those mentioned in the King file — ranging from investigators and informants to suspects and their associates — we view the very division and volatility of public opinion on these matters as ample reason for the degree of caution that the court exercised.174
Against the significant privacy interests implicated by the material in question, the District Court weighed the public interest in their disclosure. By its estimate, appellant’s announced intention of using released information to prepare a biography of Carol King’s life and work reflected a matter of “some public interest, although very minimal.”175 We think, to the contrary, the public value of such a work might be considerable in view of “the importance of Carol King in the legal and social controversies of her day [and] the lack of any extensive published history of the causes in which she was involved____”176 It was, however, appellant’s burden to support “adequately ... [her] ‘public interest’ claim with respect to the specific information being withheld.” 177 Appellant has not attempted to demonstrate how disclosure of the identities of the specific classes of persons in issue would be of moment in preparation of her book. Indeed, she emphasizes her intention to focus the book on King’s career, disavowing any “purpose to discover or write about the particular methods of surveillance that were used in Carol King’s case,” and addressing the FBI’s investigation only to the extent “that the public be [made] aware in general of the consequences that defenders of unpopular causes have sometimes been made to suffer.” 178 In this posture, we decline to dis[235]*235turb the District Court’s ultimate conclusion that the privacy interests asserted by the FBI in defense of withholding outweighed any public interest attending disclosure.179
The FBI has additionally retained material in the King file pursuant to Exemption 7(D), which safeguards from disclosure the identity of a confidential source as well as information furnished by that source.180 The District Court sustained the FBI’s Section 7(D) withholding claims in full.181 Appellant contests the propriety of this ruling on the single ground that the evidence proffered did not show sources in fact confidential in a degree sufficient to warrant summary judgment in favor of the FBI.182
The District Court having, in its words, “reviewed painstakingly each of the documents” 183 for which the FBI claimed protection by Exemption 7(D), concluded that the withholding was properly supported. As to those documents marked “confidential informant” at the time of their compilation, the court found “a clear indication” in the record that express assurances of confidentiality were afforded the informants in question.184 As to those interviews recorded in documents not so marked, the court accepted the FBI’s assertion that the information they incorporated was obtained under implied assurances of confidentiality. Recalling “the tenor of the times [in which the] investigation was conducted,” and placing particular emphasis upon the fact that “many of the informants were in close association with Ms. King and organizations which were of interest to the FBI,”185 the court reasoned that this apparent conflict in allegiance presented “a circumstance from which the implied assurance of confidentiality could reasonably be inferred.” 186
Appellant would have us overturn the District Court’s determinations on the theory that the court was not sufficiently skeptical about the FBI’s use of the “confidential informant” label during the period when the King file was compiled; and, moreover, that it too readily inferred an expectation of confidentiality on the part of interviewees who provided the FBI with what appellant characterizes as “laudatory ... or ... innocuous” as distinguished from “accusat[ory]” information.187 We decline to disturb the ruling in either re[236]*236gard. After a thorough examination of the redacted documents, the court satisfied itself that the contemporaneous identification of sources as “confidential” supplied a sound factual basis for the Exemption 7(D) claims. It is not for us to upset that conclusion where appellant can point to no countervailing record evidence that would call it into question.188
We view as equally ineffectual appellant’s challenge to the determinations on implied assurances of confidentiality. Appellant insists that no inference of confidentiality is possible because the information provided by such sources was benign in nature. We observe first that this argument derives its impetus entirely from appellant’s own characterization of the information in question, and, further, that the characterization is essentially a reflection of her skepticism of the motives and concerns animating the FBI’s investigation of Carol King. Whether appellant deems the information in question “laudatory” or “innocuous,” the FBI judged it to be of investigative significance at the time, and those the FBI interviewed most likely understood this. We reject the invitation to speculate about the circumstances of the interviews in question on the basis of the partisan analysis appellant offers. The District Court proceeded instead by first cultivating a vantage point contemporaneous with the interviews and then examining the relations and allegiences of those who gave the FBI information. We find this approach soundly reasoned, and, in view of the FBI’s general interest in honoring source expectations of confidentiality, decline to upset the court’s determinations.189 We therefore affirm the District Court’s disposition of the Exemption 7 claims, and remand the case for further proceedings on the Exemption 1 claims in accordance with this opinion.190
So ordered.