It has taken just over 50 years for the mysterious serial killer cipher codes to be finally broken by 3 hobbyist cryptographers. The 340 cipher consists of a mix of cryptic marks and alphabetical letters.
The cryptographers used a mix of algorithmic approaches and code-breaking software using modern computing power to reveal the hidden message in one of the letters sent to the press in the '60s and '70s. There are two more letters to be decrypted, one containing 13 characters and another has 32 characters.
http://zodiackillerfacts.com/news-and-updates/breaking-news-the-zodiacs-340-cipher-has-been-solved/