While one of the world's highest-profile and most intriguing ciphers was successfully cracked this weekend, two brain-melting puzzles made by the infamous Zodiac killer remain unbroken.
One of the ciphers may even reveal the biggest secret of all: the serial killer's identity.
During the late 1960s the Zodiac killer was responsible for at least seven murders, usually in lovers' lanes around the San Francisco Bay Area.
The most compelling pieces of evidence were four ciphers, or coded messages, mostly sent to The San Francisco Chronicle newspaper.
More than 50 years after the Z 340 cipher was carefully written up and sent, an international three-person team of codebreakers, including an Australian mathematician, finally figured out the message.
Over the weekend the FBI confirmed that the puzzle, which had baffled cryptologists for decades, had been cracked.
Attention now turns to the killer's two remaining ciphers.
Among law enforcement and the cryptology community, there is intense fascination over what kind of case-solving information may be locked inside.
Scores of podcasts, YouTube videos, blogs and online forums are dedicated to trawling over and over each of the ciphers.
Z 13 cipher
This puzzle, the killer's shortest cipher, was sent on April 20, 1970.
It begins with the words "This is the Zodiac speaking By the way have you cracked the last cipher I sent you? My name is ⎯⎯"
The short handwritten note is followed by 13 symbols.
Some have theorized the cipher is just a joke, and that the killer would never reveal their identity.
Claims are made and clues are shared. Discussion is lively.
One solution to the cipher claimed the name in the code was ALFRED E. NEUMAN, the mascot of the legendary US comic Mad magazine.
The first three letters in this particular cipher are A, E and N. Some believe that these letters, symbolizing the initials of Alfred E. Neuman, reinforce the Mad theory.
Z 32 cipher
The Z 32 cipher, also known as the map cipher, was sent on June 26, 1970.
Appearing at the end of a letter sent to the Chronicle, the cipher is 32 characters long.
The cipher was part of a wider puzzle, which included a roadmap of California.
At the time, the map was widely available in service stations on the west coast.
The Zodiac killer placed their signature symbol, a circle with cross hairs, on top of Mt Diablo.
It appears on the mountain as a kind of compass, with the instruction that "0 is to set to Mag. N."
Magnetic north is slightly different to true north.
The natural question was, was Mt Diablo somehow significant to the killer or its victims?
Z 408 cipher
Containing 408 characters, the Z 408 was the killer's longest cipher.
It was solved by a North Salinas schoolteacher Donald Harden and his wife Bettye.
The Zodiac killer split this cipher into three pieces and sent it to two newspapers.
They killer demanded the ciphers be printed or they would unleash a killing rampage.
The newspapers published the puzzles.
While the Z 340 took 51 years to solve, Mr and Mrs Harden solved the cipher in a week.