On June 30, 1999, sheriff’s officers in St. Louis, Missouri discovered the body of 41-year-old Ricky McCormick. He had been murdered and dumped in a field. The only clues regarding the homicide were two encrypted notes found in the victim’s pants pockets.
Pictures of notes and more details here:
http://www.fbi.gov/news/stories/2011/march/cryptanalysis_032911/cryptanalysis_032911