The FBI Indexing System

     One of the most important aspects of an FBI field office is not actually in the office: indexes. At one time, these were little more than 3 by 5 cards, maintained in scores, if not hundreds, of file cabinets in every FBI field office. For example, the New York Office of the FBI had over 7 million such cards before the system was automated. The FBI has long prided itself on information management, and under Director J. Edgar Hoover, the development of the index system was a notable first for the FBI. The Bureau had many complex rules about indexing, and laborious though it may be, it is one of the most important things an agent does. If, for example, an agent conducts an interview of a witness to a bank robbery, the person's name, address, and phone number are indexed. So, too, are the names and information developed during the course of the interview.

     This indexing is now done on a computer system, so that all FBI field offices share the same information. If, years later, only the phone number came up in another investigation, it could be traced back to the original interview. Indeed, many cases have been made or advanced over the years through the ability of the FBI to retrieve information from its own files. [When I was in the bureau, each criminal complaint that came across an agent's desk had been "indexed." That is, all names, vehicles, and addresses mentioned in the complaint that were in the index file were underlined in red. Quite often this cross referencing provided an agent with his first lead in the case.]

Joseph W. Koletar, The FBI Career Guide, 2006