>>5275666 (/pb)
Forms
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:
FD-204: Investigative report
FD-263: Cover page accompanying investigative report
FD-302: Form for reporting information that may become testimony
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.
http://www.historyofphonephreaking.org/writings/htraff/