FBI - Laboratory Services
Cryptanalysis and Racketeering Records 

Cryptanalysts
Part 1: Breaking Codes to Stop Crime

Cryptanalysts
Part 2: Help Solve an Open Murder Case

Despite extensive work by the FBI's Cryptanalysis and Racketeering Records Unit (CRRU), as well as help from the American Cryptogram Association, the meanings of the two coded notes shown at left remain a mystery to this day, and Ricky McCormick’s murderer has yet to face justice.

I've had a look at the pages and I wrote to the FBI for some more detailed photographs...

The notes don't look like a code to me, but rather appear to be a secret shorthand.
The notes are so sloppy that the "coding" must have been highly redundant and McCormick must have been able to read and write them directly, without using any complex coding devices.

A number of patterns stand out in a cursory examination:
On page 1, the three items in parentheses are quite similar, differing only in the first "words", a progression from "PQ" to "PR" and on what could be dates such as "ON DE(C) 71", "ON SE(P) 74", and "ON RE DE(C) 75." As tempting as this seems, of what significance could dates up to 40 years old have?
There are about 64 occurrences of the digraph "SE" or "5E".
"PRSE" or "PR5E" appears 5 times.
"NCBE" appears 10 times.
"WLD" appears 11 times, "W" always followed by "LD". "WLD'S" indicates it is a noun.
These numbers appear: 71, 74, 75, 194, 7, 6, 2, 26, 74, 29, 73, 35, 651, 99, 84, 52, 1/2.
"7"s are unusually abundant.
"-" appears about 11 times and appears to be a word separator.
I can't tell the difference between an "N" and a "~".  "~" sometimes seems to be a word separator.

Please email me your suggestions: nick(dot)gessler(at)duke(dot)edu.