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How to Read an FBI File

Note: This article was written by Phil Lapsley and is incorporated here with permission, due to its great usefulness in reading FBI files in the MFF Archive. See sidebar at right for more information.

Maybe you found an FBI file on the web, maybe you got it through a web site like Get Grandpa's FBI File or Get My FBI File, maybe you found it at the National Archives, or maybe it was up in the attic in great-aunt Mildred's possessions. If you're like most people, after you read it you probably had a bunch of questions. FBI files are filled with jargon, abbreviations, file numbers, codes, blacked out chunks of text, and odd little codes in the margin. Very puzzling!

If you're serious about trying to understand the stuff in that file, this document is for you. Its goal is to help you understand the contents of your FBI file. (For convenience, let's say "your file" even though the file may be about someone else.)

This document is divided into two parts. The first covers the actual content of an FBI file -- what's in it, how to make sense of FBI abbreviations, etc. The second deals with the Freedom of Information Act (FOIA), which is likely how the file you're looking at was obtained. That section will help you understand why some bits of text were blanked out, what the odd little codes in the margin mean, and give you some hints on where you can get more information.

Part I: The Contents of an FBI File

Let's talk geography for a second. (Trust me on this.)

The FBI's Headquarters (HQ, also called "The Bureau" in FBI files) is in Washington D.C. (HQ is also sometimes referred to as the Seat of Government or "SOG.") The FBI also has 56 Field Offices in major cities across the United States. Smaller offices called Resident Agencies (RAs) exist in smaller cities. Legal Attaches ("LEGATs") exist in some foreign countries.

Most of what you will see in an FBI file is messages going back and forth between Field Offices and HQ. It may help to think of an FBI file as a collection of what today would be e-mail messages. Just as e-mail messages today can range from trivial to vitally important, so too can the messages in FBI files.

Some of these messages will have been sent by teletype, others by airmail, and still others by normal surface mail. Some of the communications will be mundane or administrative while others will be more interesting. Documents in FBI files can be as serious as a "prosecutive summary" or non-prosecutive summary or something like 50+ page investigative report by a Field Office or by Headquarters which is then forwarded to military intelligence, the White House, the Attorney General or other government agencies -- and much of that data will be classified Confidential, Secret, or Top Secret. Other documents contained in FBI files include court documents, transcripts of testimony taken under oath at Congressional hearings, credit bureau reports, incorporation documents, military service records from the National Personnel Records Center, electronic surveillance transcripts, reports to and from the U.S. Secret Service, from Army, Navy or Air Force Intelligence, and security components of various agencies.

Note that most messages sent to HQ are addressed to the "Director." The Director of the FBI did not personally read every one of these messages. Rather, messages sent to HQ are processed by FBI agents assigned to the office of the Director. Similarly, messages from the Director were generally written by one of his staff members. (That said, one FBI file researcher commented that, "Anything of national significance or which might be of potential embarrassment to the Bureau or the Administration in power was routinely circulated among top Bureau officials -- including Hoover. Everything which alleged an FBI connection to some matter which might bring the FBI into disrepute or potentially involve the Bureau in some sort of political controversy was immediately sent up the food chain and seen by Hoover. It really is quite amazing how much seemingly mundane stuff Hoover initialed and often hand-wrote comments or instructions on -- including whether or not an inquiry from a correspondent should be answered and whether or not FBI publications should be sent to requesters.")

The FBI Filing System

You're going to see a lot of file numbers in FBI files, so we need to talk a little bit about how the FBI filing system works.

One of the most astonishing things about the FBI filing system is that FBI HQ and FBI Field Offices keep separate files with separate file numbers. This means that there might be a file number 87-1234 at Headquarters and it is likely completely unrelated to file 87-1234 in the San Francisco Field Office -- which in turn is probably completely unrelated to file 87-1234 in the New York Field Office! This might seem crazy today, but back before computers and the Internet when the FBI was started this was probably a pretty reasonable approach.

Because of this, a complete FBI file designator is made up of three parts:

So for example, file number 139-HQ-4992 is a file from FBI headquarters dealing with interception of communications (e.g., wiretapping) and is file number 4992 in that offense code at Headquarters. File 87-NY-6837 is fraud case number 6837 in the New York field office. Note that 87 is the offense code, not the year of the file.

HQ files are sometimes called "Bureau" files so you might see reference to "Bufile 139-4992." This is the same as 139-HQ-4992. Similarly, Field Office files are often written as something like "SF 87-1234" instead of "87-SF-1234."

A few pages marked up to indicate
file numbers
A few pages marked up to indicate
file numbers. (Click for 3-page pdf.)

You may sometimes see an offense code followed by the word "new." For example, "100-new." This indicates that the office has opened a new investigation in the 100 series (subversive matters) but that a file number wasn't yet assigned as of the time of writing.

A hypothetical Headquarters file 139-HQ-4992 might have several corresponding Field Office files, depending on where the investigation took place. If this was a wiretapping case in New York, there might be a New York file 139-NY-399 that is the Field Office file on the matter. However, sometimes the offense code in the Field Office may not match that at headquarters. As a result you sometimes wind up with funny situations like a HQ file number 139-HQ-4992 corresponding to Kansas City file 87-KC-1240.

As you go through your file you will see references to other file numbers. If you have a HQ file, these other files will frequently be Field Office files; if you have a Field Office file, you will see reference to the Headquarters file. If you are interested in learning more about the subject of your file, you will likely want to file a Freedom of Information Act request to obtain these corresponding files if you don't have them already.

A key point: Field Office files often contain significantly more information than HQ files. Consequently, the field office file should not be considered as a useless "duplicate" of HQ files. While it is true that much of the material in a Field Office file may be in a HQ file, it may have a lot that isn't there, too.

The upper left corner of reports and the lower left corner of cover pages are good places to look for file numbers. Also, most letters, telegrams, and teletype messages will have file numbers after the "From" and "To" lines. (If you click on the tiny page to the right you'll be rewarded with three pages of an FBI file that has been annotated to identify all the file numbers mentioned in it.)

It is important to keep in mind that these other file numbers do not necessarily pertain to the same subject. For example, a HQ file on Joseph Smith (100-123456) might indicate the following additional files: Los Angeles 100-2347, New York 157-2345 and Chicago 65-65192. These other files may not be specifically on Joseph Smith. Instead, they may be files which contain data about organizations or publications or some other matters deemed important for cross-referencing purposes. Perhaps the Los Angeles file pertains to an organization which Joseph Smith was involved with for some period of time, the New York file might be a file on Communist Party infiltration of that organization, and the Chicago file might be on Congressional testimony by an informant who mentioned his/her connection to Joseph Smith.)

Because file numbers mentioned in an FBI file don't always have the two-letter code showing which office the file is from, it can sometimes be tough to tell whether a file number is a HQ or Field Office file. In these cases some thought may be required to puzzle this out.

TIP: Make a list all the file numbers mentioned as you read through your file.

By the way, the offense code gives insight into the FBI's thought process during the investigation. The Field Office might have thought your file was a low-level administrative inquiry (file class 62) but the FBI Headquarters file might be something more ominous, like espionage (file class 65).


TIP: Check your serials. If you don't have all of them, try to match the missing serials up with pages listed on the deleted page sheet that followed the cover letter from the FBI.

Each document in an FBI file is called a "serial." A serial could be something as simple as a one-page teletype message or something more complex, like a 45-page report with a 3-page cover memo. Most serials are given a serial number, although a few are "unrecorded" (i.e., not given a serial number). Serial numbers typically start at 1 in each file and increase sequentially from there, though occasionally serial numbers may start with "X" and then proceed to "X-2" and then "X-3" and so on, eventually followed by serial #1. Serial numbers are frequently handwritten in the lower right-hand corner of the front of the document in large letters. They consist of the file number (without the HQ or Field Office identifier) followed by a dash and the serial number. For example, if the file number is 139-4991, serial number 3 of that file will be written as 139-4991-3.

Alas, sometimes serial numbers are illegible, or are redacted.

Serials in a file are not always in chronological order. That is, serial #1 isn't always the earliest document in the file. If this is the case for your file it may help to rearrange serials chronologically. (Also, sometimes public source materials (e.g., newspaper and magazine articles or copies of flyers or newsletters) may be put at the front of the file and given a serial number such as "1A" or "1B"; you can think of these as "sub files" of the main file.)

TIP: Account for missing pages. If you don't you can get way confused. See left for details.

It is sometimes difficult to tell if you have all the pages in a given serial, especially since the FBI FOIA team may have withheld some pages in their entirety. One trick is that usually the FBI is pretty good about putting an asterisk after the last page number of a document. So if you look at the bottom of the page and see "3*" in the center it tells you that this is page 3 of a 3 page document.


Most documents in an FBI file are titled or "captioned" with information on the file subject. A caption generally consists of three lines: the name of the subject, the character or nature of the case being investigated (often a cryptic abbreviation), and the office of origin ("OO"). So a caption might look like:

Joe Blow, a.k.a.
OO: San Francisco

This tells you that the case concerns somebody named Joe Blow who is also known by other names ("a.k.a."; sometimes the abbreviation "was" for "with aliases" is also used) and that Mr. Blow is being investigated for interstate transportation of wagering information (ITWI) and interstate transportation of stolen property (ITSP). The office of origin (OO) is San Francisco. Sometimes there can be more than one office of origin, e.g., if a suspect moves. A secret decoder ring for some of these abbreviations is available at abbreviations.com.


One thing you will quickly notice is that the FBI was, and is, crazy about forms. Are you interviewing an informant? Fill out an FD-209. Visiting a foreign country? Fill out an FD-473. The good people at The MemoryHole have obtained a comprehensive list of FBI forms under FOIA, but some of the most common you're likely to run into are:

Another document you may run into is a "letterhead memorandum", abbreviated LHM. This is an official FBI memorandum that was expected to be shown to someone outside the FBI.

Abbreviations and Jargon

FBI files are rife with abbreviations and FBI jargon. A pretty good list of FBI abbreviations is available at abbreviations.com. A shorter list of some of the more common abbreviations is at the end of this document.

One abbreviation which you may find puzzling when you first encounter it is "RUC." Literally this stands for "referred upon completion" but that doesn't quite explain what it means. It typically is used when HQ or a Field Office requests another Field Office to investigate something: when the Field Office is finished it will respond with something like "We are placing this matter in RUC status" which is FBI-speak for "Okay, here's the stuff you asked for. We're done with this unless you tell us differently."

Symbol Sources

Depending on the nature of your file, you may run into the phrases "symbol source" or "non-symbol source." The FBI sometimes uses informants or technical sources of information (such as microphones or wiretaps) when conducting an investigation. To protect the identity of these sources in some cases the FBI will replace the sources names with an abbreviation called a symbol, e.g., T-1, T-2, etc. Big surprise: these are called symbol sources. Sources not so protected are called non-symbol sources.

"June Mail"

If you're lucky :-) you may run into mention of "June Mail" in your file. According to Unlocking the Files of the FBI, "June Mail was information received from or relating to the FBI's 'most sensitive sources,' including governors, secretaries to high officials, extremely confidential information, and 'highly confidential or unusual investigative techniques'" (e.g., black bag jobs).

Mail Covers

A mail cover is a investigatory technique in which the names and addresses of a subject's mail correspondence are recorded. Mail covers don't actually open someone's mail but they do make a record of all the subject's incoming and outgoing mail.

Correlation Summaries

On files of major significance, the Bureau often prepared a "correlation summary" which essentially is a chronological history of data contained in the file. This is extremely important because often the correlation summary identifies cross-references and related files that contain information about the subject which is not always released when the main file was processed.

Part II: FBI Files and the Freedom of Information Act (FOIA)

This section deals with things you'll see in your file that are not part of the FBI file itself but are rather artifacts of your file having been processed by the FBI under the Freedom of Information Act (FOIA).

Why Does My File Look Like Swiss Cheese Sprinkled with Gibberish?

Swiss cheese sprinkled with gibberish
Swiss cheese sprinkled
with gibberish.
(Click for larger image.)

If your FBI file was obtained under FOIA the FBI almost certainly withheld -- "redacted" -- some information. (The image to the right gives an example of this; click to get a larger version.) The way the FOIA law works is that you are entitled to a complete copy of any Government file or document except for portions of the document that are exempt from disclosure. These "exemptions" are spelled out in the FOIA law; the FBI isn't supposed to redact information just because it feels like it.

(That said, several FBI FOIA researchers I spoke to gave low marks to the FBI for "routinely excising" materials, such as data already in the public domain or things that might be embarrassing to the Bureau, "just because they feel like it." See Gimme Some Truth: The John Lennon FBI Files by Jon Wiener for one man's quest to get the FBI to reveal information withheld from a famous file.)

The withheld parts are generally easy to spot: they're the big white boxes where something should have been in the file! In some cases entire pages, or dozens or hundreds of pages, may be withheld.

. . .

Whenever the FBI withholds information, it has to tell you which exemption -- that is, which part of the FOIA law -- it relied upon to withhold the material. It does so by noting the specific exemption code, which it typically puts in the right margin of the page -- just like to the right of this paragraph. These look like little letter-number abbreviations like b2 or b7c. These refer to the specific section of the Freedom of Information Act that allows the FBI to withhold this information. For example, b2 refers to 5 USC 552(b)(2). The EEOC (of all places!) has a nice summary of FOIA exemptions (see section XI).

You care about the exemption codes for a couple of reasons. First, they give you an indication of the sort of information that was redacted. Second, you can infer from them what your chances are of obtaining the redacted information if you wanted to appeal the FBI's decision to withhold it. For example, national security redactions are sometimes reversed on appeal, but redactions dealing with protecting the identity of an informant or confidential source are reversed much less frequently. Third, should you choose to appeal the redaction, the exemption will strongly influence how you write your appeal request.

Security Classifications

classification notice

Does your document have an interesting message like that to the right? "All information contained herein is unclassified"? That tells you that at one time the page you're looking at was classified and has been through a security declassification review.

Some Reference Material

The following materials may help you as you read through your file:

Finally, let's not forget:

Handy Table of Commonly Used FBI Abbreviations

ADICAssistant Director in Charge
AMAir mail
AUSA Assistant U.S. Attorney
ELSUR Electronic surveillance
FBW Fraud By Wire
FNU First name unknown
FISUR Physical surveillance
IGA Interstate gambling activities
IOC Interception of communications
ITAR Interstate transportation in aid of racketeering
ITSP Interstate transportation of stolen property
ITWI Interstate transmission of wagering information
LCN La Cosa Nostra
LNU Last name unknown
MNU Middle name unknown
RExxTEL Regarding telegram from the XX office (where XX will be an office code, see Table 2)
RExxLET Regarding letter from the XX office (where XX will be an office code, see Table 2)
RM Registered mail
RUC Referred upon completion
SA Special Agent
SAC Special Agent in Charge
SUREP Submit report
SUTEL Submit teletype summary
UACB Unless advised contrary by Bureau
UNSUB Unknown subject


Thanks to Michael Ravnitzky and several individuals who wish to remain nameless for reviewing and commenting on this article.

Comments? Suggestions? Questions?

This document is a work in progress. I'd love to hear your suggestions, comments, or questions. Please drop me a note at history-of-phone-phreaking (at) lapsley.org. Thanks!

About this Guide

Phil Lapsley wrote this article after slogging through hundreds of FBI files as research for his book on the history of phone phreaking. Please drop him a note if you have questions, comments, or suggestions. Last updated September 4, 2008.

Quick Links

List of FBI offense codes. The first digits of any FBI file designation indicate the kind of offense the FBI was investigating when it opened the file. For instance Oswald's 105-82555 file begins with 105, the code for Foreign Counterintelligence.

List of FBI office abbreviations. For instance, WFO stands for Washington Field Office, and DL for the Dallas Field Office.

List of FBI Abbreviations. For example, ASAC is short for Assistant Special Agent in Charge.

FBI Records in the MFF Archive

FBI Files on JFK Assassination. Includes Oswald and Ruby files, main JFK assassination investigation file, Warren Commission liaison file, HSCA administrative folders and subject files, and more. Over 500,000 pages in total.

FBI MURKIN Files. FBI records on the assassination of Dr. Martin Luther King, Jr.

FBI LAFO RFK Files. Los Angeles Field Office files on the assassination of Robert F. Kennedy.

Note: Many FBI records on the MFF website have a second identifying record number, the standard National Archives RIF number. These are all 13-digit numbers beginning with the FBI designator 124, for example 124-10003-10388. The discussion in this article refers to the FBI's internal filing numbers, not the National Archives RIF numbers.

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