Col. Mark Adger/Business Insider/Mark Abadi
This coded letter from an inmate, intercepted by staff at Fulton County Jail in Atlanta, secretly ordered a hit on a staff member.
- In jail, inmates often rely on secret codes to slip messages past corrections officers.
- Cracking these codes is the specialty of the FBI's cryptanalysis unit.
- We compiled some of the most common jail codes, as well as one the FBI never solved.
In jail, corrections officers are constantly monitoring the mail inmates send and receive.
They're looking for any number of things hidden in the envelopes - drugs, money, or contraband items like cell phones, for example.
But in many cases, they're looking for something much harder to spot: secret codes.
That was the case last year at Fulton County Jail in Atlanta, when staff intercepted a letter from an inmate that looked innocuous, but actually contained an encoded message ordering a hit on a staff member.
Cracking codes is the specialty of the FBI's Cryptanalysis and Racketeering Records Unit, which details on its website the various types of secret codes, or ciphers, used by inmates.
We've compiled some of the most commonly used codes below: