Ricky McCormick's encrypted notes are two hand-written documents found in the pockets of murder victim Ricky McCormick when his body was discovered in a field in [https://en.wikipedia.org/wiki/St._Charles_County,_Missouri St. Charles County, Missouri, on June 30, 1999. Attempts by the FBI's Cryptanalysis and Racketeering Records Unit (CRRU) and the American Cryptogram Association failed to decipher the meanings of those two coded notes, which are listed as one of the CRRU’s top unsolved cases. On March 29, 2011, the U.S. Federal Bureau of Investigation issued an appeal for help from the public in obtaining the meaning of the messages. A few days later, they updated their website to note the "outpouring of responses", and established a separate page where the public can offer comments and theories.
More information on the Wikipedia page