Shown here is an early FBI Firearms Lab report revealing the results of an exam conducted by SA Charles Appel.  Appel in 1934 was nearly a "one man army" in the FBI Lab which was only established in 1932.  Although he was predominantly a document specialist, Appel appears to have handled most of the gangster type weapons exams sometimes with the assistance of SA Sam Pickering. 

From an examination of these lab reports, each section reveals critical information on the evidence.  What the specimens submitted actually are; the date it was submitted and by whom, (in this case the St. Paul Bureau Office); where the evidence was obtained from; who conducted the exam; the results and where copies and photos of the evidence were being kept or sent.  The case file number would always appear in the upper right and in the Dillinger case it began with the number "62."  Later on, the FBI Lab examiners would begin utilizing the letter "Q" with numbered evidence revealing it was a "questioned" item as opposed to a "known item."  

The first grouping of numbers in an FBI file number reveals what kind of case it is.  In 1934, a "62" case was a Stolen Motor Vehicle Case.  As years progressed, "88's" were fugitive cases; "91's" were bank robberies and so on through the list of some 200 plus Federal violations.

So, at any time an Agent in the Field could have a "search" done of the "indexing records" on a particular name.  If we searched the name of Dillinger for example, and found (2) 62 cases; (1) 88 case and (4) 91 cases, it would immediately tell us that Dillinger had been the subject/involved in 2 Motor Vehicle cases; 1 case of being a fugitive and 4 cases of bank robberies.  An immediate clue you were dealing with someone with a long record.   

The Bureau in 1934 was well tuned into the various local police departments around the country and made these results and any photos available to them on a routine basis.  By departments submitting ballistics to the FBI Lab at the time, the Lab could (as basically a "clearing house") determine if the weapon, bullets or cartridges matched crimes in other jurisdictions the police were unaware of. 

It is interesting to note that upon examining this and other Lab reports of the '30s, when I retired in 2003, the Lab Reports as you see here, with exception of some very minor changes, stayed the same!