Follow leads, read articles and attempt to crack a case that remains unsolved to this day.
A 19th-century wife killer crafted poetic looking ciphers; a 21st-century serial child murderer used encrypted computer files.
Is this what the Zodiac Killer would have sounded like?
Some have been broken, while others remain stubbornly resistant to code-crackers.
The elusive killer has never been found.
Here's why they were suspected—and why they were ruled out.