9. Every file has a serial number made up of numbers and letters. The first number is always the “class” number, or the code for the type of offense the FBI was investigating. In this case, the “class” is “9” which is code for “Extortion.” Any letters indicate the field office where the investigation was taking place. The second set of numbers is the file number, which in this case is “58051.” For a complete list of FBI “class” codes, go to: www.newstrench.com/ 03secret/0categories.html