Mathematics: the encrypted messages of the “Zodiac Killer”

The fourth cryptograms of the Zodiac Slayer are designated Z408, Z340, Z32, and Z13 based on their lengths. A priori, the longest must be the easiest to decipher… and it was. It was sent in three pieces of 8 lines and 17 columns, of which here is the first.

Message Z408

A quick look shows that it is not a mono-alphabetic substitution, where each letter of the alphabet is replaced by one and the same symbol, because it contains about fifty different symbols, much more than 26 The simplest hypothesis is that frequent letters, like the “e”, have been encrypted in several different ways. In other words, we are probably dealing with a homophonic cipher, such as that of Mary Stuart and other Renaissance sovereigns. History teaches us how to decipher such a cipher: the probable word method, invented by Giambattista della Porta (1535 – 1615). It consists of looking for words whose presence is probable in the text.

This first letter, Z408, was decrypted by a teacher and his wife, Donald and Betty Harden. Their idea was to go into the psychology of a serial killer who, according to them, has an overdeveloped ego… so the message had to start with the letter “I” which, in English, means “I”. Then they searched for “kill” and “killing” which correspond to the verb “to kill”. The code then crumbled little by little. Here is the decrypted message:

I LIKE KILLING PEOPLE BECAUSE IT IS SO MUCH FUN IT IS MORE FUN THAN KILLING WILD GAME IN THE FORREST BECAUSE MAN IS THE MOST DANGEROUS ANAMAL OF ALL TO KILL SOMETHING GIVES ME THE MOST THRILLING EXPERENCE IT IS EVEN BETTER THAN GETTING YOUR ROCKS OFF WITH A GIRL THE BEST PART OF IT IS THAT WHEN I DIE I WILL BE REBORN IN PARADICE AND ALL THE I HAVE KILLED WILL BECOME MY SLAVES I WILL NOT GIVE YOU MY NAME BECAUSE YOU WILL TRY TO SLOI DOWN OR STOP MY COLLECTING OF SLAVES FOR MY AFTERLIFE EBEORIETEMETHHPITI

Note that the many spelling mistakes were probably intentional, a skill of the zodiac. A text containing spelling errors is indeed more difficult to decipher! We can translate the text like this:

” I like killing people because it’s fun, more than killing game in the forest, because man is the most dangerous animal of all to kill. It’s exciting, even more than having a good time with a girl. The best will be when I die. I will be reborn in paradise and all those I have killed will become my slaves. I won’t give my name because you would try to slow down or stop my harvesting of slaves for my afterlife. Ebeorietemethhpiti. »

Unfortunately, despite what he had announced to the police, his signature remained incomprehensible. He also announced himself why he did not give his name. A delirious reason which one can doubt that the killer believed in it.

Message Z340

This rapid decryption may have upset the Zodiac, who wanted to show off their abilities by sending a more difficult to decrypt message, the Z340. And it was, since it took 51 years and three people to do it: David Oranchak, a IT Developer American, Sam Blake, an Australian mathematician and Jarl Van Eykcke, a passionate about cryptography Belgian.

The symbols used are of the same nature as those of the Z408, so part of the encryption is probably a homophonic substitution. Another cipher had been added to it otherwise Z340 would have been decrypted long ago. The story of the cryptography suggests to us that it is a transposition, an anagram of the message… which does not mean that it is easy to find. This takes us back to the First World War where the best figures combined substitution and transposition.

Before tackling the transposition, it is normally necessary to find at least part of the substitution. It didn’t work in this example and the decryption team looked for a transposition that was easy to operate by hand.

In fact, the trio discovered (by chance according to them) that the text was split into three parts (twice 9 lines then 2 lines) and the sequence of letters in each part describes the movement of a knight in chess (more precisely, two squares to the right and one down) starting from the top left. When the right edge is reached, the move continues to the next row to the left.

The team of decryptors then used the software AZdecrypt created by Jarl Van Eykcke, which allows to decrypt homophonic substitution ciphers. After a large number of tries, comprehensible pieces of text appeared diagonally, much like in the Bible code of Eliyahu Rips (except that here it cannot be a coincidence).

The decrypted text is:

I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME THAT WASNT ME ON THE TV SHOW WHICH BRINGS UP A POINT ABOUT ME I AM NOT AFRAID OF THE GAS CHAMBER BECAUSE IT WILL SEND ME TO PARADICE ALL THE SOONER BECAUSE I NOW HAVE ENOUGH SLAVES TO WORK FOR ME WHERE EVERYONE ELSE HAS NOTHING WHEN THEY REACH PARADICE SO THEY ARE AFRAID OF DEATH I AM NOT AFRAID BECAUSE I KNOW THAT MY NEW LIFE IS LIFE WILL BE AN EASY ONE IN PARADICE DEATH

We can translate the text like this:

” I hope you have fun trying to catch me. It wasn’t me on TV, which leads me to say something about myself: I’m not afraid of the gas chamber because it will send me to heaven sooner because I’ve had enough now. slaves to work for me while all the others have nothing when they arrive in paradise: that’s why they have fear of death. I’m not afraid because I know my new life will be easy in the afterlife, in paradise. »

In this text, the Zodiac alludes to an October 1969 television program in which a man claiming to be the Zodiac Killer intervened by telephone. Of course, it wasn’t him.

Beyond the Numbers

Fifty years have passed since the first murders and the decryption of the letters of the zodiac will undoubtedly bring nothing to the investigation. The criminal always hides behind his composite portrait and his acronym. Maybe he’s dead or in prison for another case? Perhaps he now lives a peaceful life? We will probably never know.

A rebound ?

In April 2021, an article appeared in “La Jaune et la Rouge”, the journal of former students of the polytechnic school announcing the decryption of “the last three coded clues left by the killer” by Fayçal Ziraoui from the class of 2003. Of course , Ziraoui’s approach is exposed there. Quite rightly, he notices that the register of the last messages is that of the treasure hunt. Their decryptions will have to be judged in this register, that is to say by the advances they allow. Z32 announced a bomb to be unearthed 50 years ago to avoid the destruction of a school bus. No bomb having exploded, one can doubt its reality. On the other hand, we can hope for an advance in the decryption of Z13 which, according to the killer, gives his name in the form of a cryptogram of 13 letters.

Here it is : NEA⊕@K@M@λNAM

According to Ziraoui, the name indicated would accuse one of the suspects, Lawrence Kane … which is not enough to convict him.

References

Herve Lehning, The Secret Code BibleFlammarion, 2019.

David Oranchak, http://www.zodiackillerciphers.com

Robert Ranquet, Interview with Fayçal Ziraoui, La Jaune et la Rouge, April 2021