It would be befitting that the Zodiac Killer's last correspondence may possibly be the 'Eureka' card mailed in the December of 1990, considering the last major work of Edgar Allan Poe was the non-fiction offering Eureka: A Prose Poem.    
"Adapted from a lecture he had presented, Eureka describes Poe's intuitive conception of the nature of the universe with no antecedent scientific work done to reach his conclusions. He also discusses man's relationship with God, whom he compares to an author. Similar to his theories on a good short story, Poe believes the universe is a self-contained, closed system. In coming to his conclusions, Poe uses ratiocination as a literary device, through his character C. Auguste Dupin, as if Poe himself were a detective solving the mystery of the universe. Eureka, then, is the culmination of Poe's interest in capturing truth through language, an extension of his interest in cryptography. Some modern critics believe Eureka is the key to deciphering meaning in all Poe's fiction, that all his works involve similar theories." Wikipedia. Strange therefore, that the Christmas card possibly engineered by Zodiac should contain a cryptic message in the form of photocopied keys mailed from Eureka, California.
This is not the only time that Edgar Allan Poe may have played a part in a cryptic message mailed by the Zodiac Killer. It could have been the essay 'A Few Words on Secret Writing' that inspired the creation of the '13 Symbol' cipher mailed on April 20th 1970 by the Bay Area murderer. A cipher that was devised sometime between October 22nd 1969 and November 8th 1969, and belatedly mailed by the killer some 6 months later, with the accompanying text about the murder of San Francisco police officer Brian McDonnell on February 16th 1970. Secret Writing from our Secret Pal.      

Michael Cole wrote an excellent article entitled "My Name Is" Cipher Motivation that suggested the Zodiac Killer likely drew his inspiration for the '13 Symbol' cipher from an October 22nd 1969 newspaper article by Will Stevens, which laid down a challenge to the Zodiac Killer from the president of the American Cryptogram Association (ACA), Professor D.C.B. Marsh, to reveal his name. Apparently, several months later the killer duly obliged by opening his correspondence with the line "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is...." 
He followed this by placing 13 characters underneath, widely believed to be the Zodiac Killer offering us his name. 
One couldn't help considering whether this cipher was not only created because of the newspaper article, but whether this cipher was created based on what was contained within the article- in particular the works of Edgar Allan Poe. This would be right up Zodiac's alley, devising a cipher based in the text of the newspaper article. 
Here is an excerpt "Dr Marsh told the Examiner today: "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in the cipher to established cryptogram experts. He knows, to quote Edgar Allen Poe, that any cipher created by man can be solved by man. Zodiac has not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald. Zodiac has not done this, because to tell the complete truth in relation to his name-in cipher code-would lead to his capture. I invite Zodiac to send The American Cryptogram Association a cipher code, which will truly and honestly include his name."

We can see in the Edgar Allan Poe essay 'A Few Words on Secret Writing,' at the very beginning he shows the alphabet being split into two halves of 13 letters:
"Were two individuals, totally unpractised in cryptography, desirous of holding by letter a correspondence which should be unintelligible to all but themselves, it is most probable that they would at once think of a peculiar alphabet, to which each should have a key. At first it would, perhaps, be arranged that a should stand for z, b for y, c for x, d for w, &c. &c.; that is to say, the order of the letters would be reversed. Upon second thoughts, this arrangement appearing too obvious, a more complex mode would be adopted. The first thirteen letters might be written beneath the last thirteen, thus:
n o p q r s t u v w x y z
a b c d e f g h i j k I m; and, so placed, a might stand for n and n for a, o for b and b for a, &c. &c. This, again, having an air of regularity which might be fathomed, the key alphabet might be constructed absolutely at random." 

Quite fortunate that the Zodiac Killer, after possibly reading this newspaper article, should then create a cipher of 13 characters beginning with an A (the first letter of the alphabet) and ending with an M (the 13th letter of the alphabet), just like Edgar Allan Poe's construction in his essay 'A few Words on Secret Writing.'  
Throughout the newspaper article Professor D.C.B. Marsh is urging the Zodiac Killer to give his name, which clearly he wasn't going to achieve with such a limited number of characters, but he may have played a game with D.C.B. Marsh by offering us another cryptic message within the cipher. We contended previously that the 340 cipher and '13 Symbol' cipher were both likely created at the same time because of the interconnectivity between the two. The name Zodiac appeared to be numerically carried forward from the 20th line of the 340 to the '13 Symbol' cipher in the form of three circled 8's. This was achieved by placing the correct spelling of Zodiac alongside the 'near Zodiac' and numerically counting the difference between the columns. This produced perfect numerical symmetry, as did placing A to M (half the alphabet) alongside the '13 Symbol' cipher. For this to be achieved, it was argued the two ciphers must have been created with each in mind, and therefore both devised before November 8th 1969. See image here for explanation or read article 'Heaven Sent'.  
"In Christian numerology, the number 888 represents Jesus, or sometimes more specifically Christ the Redeemer. This representation may be justified either through gematria, by counting the letter values of the Greek transliteration of Jesus' name, or as an opposing value to 666, the number of the beast. "  
Wikipedia.
Curiously, if you visit the English gematria site here and enter Edgar Allan Poe into the calculator, 666 is achieved.    
​Was the Zodiac Killer playing games, giving us the name Jesus in the form of a numerical value and depicting himself as the savior of souls for the afterlife.

Professor D.C.B. Marsh attempted to coerce the Zodiac into giving us his name by stroking his ego- so it seemed rather unusual that every alphabetical letter within the '13 Symbol' cipher apart from one, could be found in the word 'NAME'. The Zodiac Killer gave us A twice, M twice, N twice and E once. The only exception was the letter K- the only letter the Zodiac Killer scrubbed out in the 340 cipher. Removing this from the '13 Symbol' cipher only leaves us with letters contained in the word NAME.
The creation of these two ciphers together is the only reasonable explanation for a correlation between the two (if one exists), and the inspiration of Edgar Allan Poe in the construction of the '13 Symbol' cipher, based upon splitting the alphabet down its center, was ultimately born from the article by Will Stevens.
​Edgar Allen Poe stated that "any cipher created by man can be solved by man."
Could it be that, any cipher created by Zodiac can be solved by Edgar Allan Poe.

This is a combination of previous articles (with a little extra) under one banner, attempting to dispel the idea that the 340 code is a genuine cipher, and all attempts at trying to reveal a continuous and coherent message will ultimately fail. 
By overwhelmingly consensus, the 340 cipher will soon be entering its 50th year unbroken, remaining impervious to all attempts at releasing its secrets, despite innumerable attempts by the best codebreakers and codebreaking machinery thrown at it. Either the Zodiac Killer created a cipher so stunningly impossible and misjudged the complexity of his cipher, or he didn't create one at all. The '13 Symbol' and '32 Symbol' codes were simply too short, with too many variables to be broken by conventional means. The '32 Symbol' cipher has 29 unique characters, meaning you can literally fill in the blanks however you choose. The '13 Symbol' cipher is simply too short to be called a cipher, and any solution proffered can be readily dismissed without a valid key. The Zodiac certainly wasn't stupid and must have known this- pouring huge doubt on whether he ever intended them to be solved in a conventional manner. Therefore, why should we treat the 340 cipher any differently. The whole thing just appeared to be one big game for the Zodiac Killer, as we huffed and puffed long into the night trying to pry open his ultimate masterpiece.
Many observers have wondered whether the Zodiac Killer mailed the 'code key' to the Vallejo Police Department on August 10th 1969 under the guise of a "concerned citizen," unaware that it had already been solved by Donald Gene and Bettye June Harden, as well as the FBI in Washington. Unusual that he should then sit on the 340 cipher for many years to come, able to resist the temptation of revealing his subsequent ramblings. Keeping a secret for nearly 50 years would certainly take great restraint from a killer who bathed in the spotlight.
The 340 cipher may very well have been designed in the mind of the killer as early as August 4th 1969, or the moment his 408 cipher was cracked. The decrypted 408 read: "I like killing people because it is so much fun it is more fun than killing wild game in the forest because man is the most dangerous animal of all to kill something gives me the most thrilling experience 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 (people) I have killed will become my slaves I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife." 
The answer to the 340 cipher probably already lay within the text of the 408 cipher- just designed in an altogether different format. The clue would later reveal itself in the design of the 'Halloween' card, mailed on October 27th 1970, where the killer placed "Paradice" and "Slaves" in a cross formation, and told us "sorry no cipher." This wouldn't be the only time the Zodiac Killer gave us clues, alluding to the fact we were chasing a solution to a cipher that didn't exist.        

One of the best finds in recent years was by Tahoe27, a regular contributor to the Zodiac Killer Site forum, who discovered a connection between a Tim Holt comic and the 'Halloween' card. Many features on the cover of the comic parallel the 'Halloween' card, including the wording By Fire, By Gun, By Rope and By Knife, along with "Redmask" (the skeleton eyes) and "Lady Doom" (peek-a-boo you are doomed). However, I believe Tahoe27 is not convinced that the 'Halloween' card was authored by the Zodiac Killer. 
If the 'Halloween' card was authored by an impostor, who based the 'Halloween' card on the Tim Holt comic, then are we to believe he was extremely fortunate that a year earlier, the real Zodiac Killer just happened to create a 340 cipher containing the word "BY" in all four corners of the cipher, along with PARADICE and SLAVES being a possibility, running down and across the cipher on the midpoint vertically and horizontally, just like the configuration on the 'Halloween' card.
Admittedly, the words paradice and slaves have not been proven to exist in the 340 cipher, but the fact they are a distinct possibility by comparison to the 'Halloween' card appears another very fortunate stroke of luck- particularly if we believe the author of the 'Halloween' card wasn't the Zodiac Killer- and only considered the Tim Holt comic in his design of the 'Halloween' card. If the 'Halloween' card was crafted by the Zodiac Killer using only the Tim Holt comic, then the above still applies.
The more likely conclusion we could draw from this, is that the 340 cipher was designed with the Tim Holt comic in mind, and the 'Halloween' card (one year later) was giving us a clue.  

​On the right, we can see how the four words "BY" fit into each quadrant of the 340 cipher just like the 'Halloween' card offering. What are the odds that in each quadrant of 80 characters we would find the letters B and Y together either horizontally or vertically every time. Not to mention the fortunate appearance of paradice and slaves bisecting the cipher perfectly. The killer may even have given us his signature in the bottom right corner, along with the running total, which was seven and counting on November 8th 1969.
If this wasn't the intended design of the 340 cipher, then either the Zodiac Killer or an impostor got extremely lucky, in just happening upon a Tim Holt comic that mirrored the 340 cipher unintentionally. But we may just be able to prove a definite link between these two communications and confidently state that both were designed by the Zodiac Killer, and with a fair degree of confidence, argue that the 340 cipher is not a cipher in the true sense of the word. The majority of the characters likely filler, but in this instance, far more than the 18 characters at the foot of the 408 cipher. The reason we may be able to contend the 340 cipher is not a continuous and uniform message like the 408 cipher (and not a cipher as we believe one to be), is because the Zodiac Killer lined us up for a fall and then admitted to it a year later.
On the 'Dripping Pen' card accompanying the 340 cipher, the killer stated
"This is the Zodiac speaking. I though you would nead a good laugh before you hear the bad news. You won't get the news for a while yet. Could you print this new cipher in your frunt page? I get aufully lonely when I am ignored, so lonely I could do my Thing." Was that bad news to come on October 27th 1970, when he mailed the 'Halloween' card.
If we believe that the 'Halloween' card design is referring back to the 340 cipher, then the message concealed on the envelope inner of "sorry no cipher," is the Zodiac Killer finally admitting that the 340 cipher is not the real cipher we had thought.
He is declaring that the 340 is "no cipher," and is in fact, based upon the paradice and slaves configuration. This is why he crosses the phrase "sorry no cipher" to mimic the design of paradice and slaves, using 13 letters in both instances.
The Zodiac Killer could easily have written "sorry no cipher" just the once, but deliberately fashioned it to form a link between the 'Halloween' card design and the 340 cipher.
After searching for solutions to the 340 cipher for nearly half a century, the Zodiac Killer may have given us the answer to its design after just one year, but it was overlooked. We have took the phrase "sorry no cipher" as an apology, that he wasn't giving us a cipher in the 'Halloween' card, when in actual fact, he was apologizing for stringing us along for the best part of a year, and offered us the real solution to the 340 cipher on October 27th 1970, contained within the 'Halloween' card. You could say it was a "trick" and "treat" befitting of Halloween.

​You will notice that the paradice and slaves configuration from the 'Halloween' card fits nicely into the 340 cipher.
The two dashes on the 10th line are represented by the letter S. 
The left-facing V on the 9th column and 10th line are represented by the letter E. 
​The two addition signs on the 9th column are represented by the letter A.
When the letter R of paradice is placed into its only conceivable position, along with the L and V from slaves, it is reminiscent of the 'Halloween' card. What are the chances that this could be achieved accidentally?  

The word paradice travels vertically 17 lines, exactly matching the 17 columns that slaves travels horizontally.The Zodiac Killer placed crosshairs beneath the 9th column, the midsection of the cipher (shown here).
The intersection on the 'Halloween' card configuration forms RAD and LAV, exactly the same as the bisecting center point of the 340 cipher. The Zodiac Killer also underlined the LAV of Paul Averly on the Halloween card envelope, on which he also placed the intersecting "sorry no cipher" on the envelope inner. 
The 'Halloween' card stamp depicts the surface of the moon with a half-earth in the distance and the words "In the beginning God." This phrase fits perfectly on the 1st line (the beginning) of the 340 cipher, with the 15th, 16th and 17th characters uncannily similar to the word GOD (the O in half phase just like the image on the stamp). 

But this wouldn't be the only correspondence that suggested the 340 cipher was designed as a puzzle rather than a 408 style message, If the paradice and slaves connection does exist between the 340 cipher and 'Halloween' card, then it makes more sense that the design of paradice and slaves was created in the 340 cipher first, and the 'Halloween' card was to "clue us in". If not, then the observation is just happenstance.
​If the 340 cipher doesn't actually contain a message, it will never be broken, and paradoxically will remain unsolved despite no solution being possible. 
The cipher has many other issues- in that, the Zodiac Killer may have had 'cipher three' formulated or drafted before he designed 'cipher two', to enable the interconnectivity between both. He had to think forwards to create backwards.
If we assume the 340 cipher has a solution and therefore a key (no matter how complex), then one may assume the Zodiac created the key, then created the message, and then applied the message to the key, so as to encrypt it. If this were the case, we must believe that the 'near Zodiac' that emerged on line 20 was by sheer chance. We would also have to believe, that had he crafted 'cipher three' completely independent of 'cipher two', with no intention of connecting both, then the following observations also happened completely by chance.

​Although covered many times before, the following will help explain the conundrum. 
Because the '13 Symbol' cipher was thirteen characters in total (half the alphabet) and began with an A and ended with an M, it was considered that by placing the first half of the alphabet alongside the '13 Symbol' cipher and numerically counting the difference between the columns, something may emerge- It did.
For example: C to N produces a difference of 11, whereas B and E produces a difference of 3. Non alphabetical symbols cannot produce a difference, so a zero is inserted. The resulting numbers produced have been color coded. The red section is before the first circled 8, the green section is after the last circled 8 and the blue section spans the first and last circled 8. Notice the perfect symmetry. The red and green numbers are identical read forwards or backwards, and the blue numbers again read identically in either direction, producing a mirror image.
An equally symmetrical pattern was created using the identical technique, when placing the correct spelling of Zodiac alongside the 'near Zodiac' on line 20 of the 340 cipher. 
Furthermore, the three 0's and three 8's created, can be combined and carried forward onto his '13 Symbol' cipher, which seemingly is what he did.
It is also apparent on the '13 Symbol' cipher, that either side of the three circled 8's are the Zodiac crosshairs and an inverted Aries symbol, also present on either side of the 'near Zodiac' on the final line of the 340 cipher. So, the author has effectively carried eight symbols from one cipher to another.
The point being, that when the Zodiac Killer sat down at his desk and began to create a unique key for his 340 cipher, into which he was to place his message, it accidentally created the 'near Zodiac' on the 20th line, accidentally created the correlation between 'near Zodiac' and Zodiac to produce three circled 8's, accidentally created the symbols either side of 'near Zodiac,' that fully or in part, carried forward to the '13 Symbol' cipher in the correct position, and accidentally created symmetry in both instances. Or, the Zodiac crafted the '13 Symbol' cipher before or alongside the 340 cipher, which I would argue nobody believes.
The Zodiac Killer may have began his 340 cipher key from the bottom first, deliberately allocating specific letters in his message to create the 'near Zodiac' characters and continuing from there. But, if the interconnectivity exists between the 340 cipher and '13 Symbol' cipher, he effectively began with 'cipher three' first and worked backwards, and worked forwards with the words ​paradice and slaves from the 408 cipher. 

​The Zodiac may have presented us with a fictitious negro male on August 4th 1969, who by inference, provided us with some valuable information about the Zodiac Killer driving his brown car by the payphone at Springs and Tuolumne. Was this a red herring of a clue, much like the correction on line 6 of the 340 cipher.
It can be clearly seen on the left, that the Zodiac Killer was conscientious enough to correct an alphabetical K to a reversed K on line 6, even though spelling correctly was never much of an issue with the Zodiac Killer. To validate that this was a genuine mistake, he made sure that the original K had not been fully obscured. This may give the impression it is easy to mix up your K's when implementing your encrypted text. Or maybe this is what he wanted us to believe. Who in their right mind would correct a fake cipher? Therefore it must be genuine.
Did the Zodiac Killer implement this correction, conveniently leaving the blacked out character still visible (and just reversing it), to give us the impression that the 340 cipher is undeniably genuine. Was this move just another red herring, to again validate something that never was. 
Alternatively, the final line of the 340 cipher may contain just a part message, yet incomplete, bearing in mind that many believe the '13 Symbol' cipher may contain some form of a name. The 340 cipher may end with: "the Zodiac is".... to be continued on the next cipher. The anticipation of the newspapers and readers alike, for the sequel to be released, would be a Zodiac dream.
The Zodiac Killer may have been pushing us in the right direction on October 27th 1970, but his attempt at revealing the workings of the 340 cipher may have begun far earlier, on December 16th 1969- just 38 days after his 'so called' masterpiece- in which he would be claiming a potential 38 more victims.
The December 16th 1969 'Fairfield' letter, mailed to the San Francisco Examiner, has been considered dubious Zodiac correspondence, however, it may have been Zodiac's first foray into revealing the mechanics of the 340 cipher, albeit using a rudimentary code as a tool. 
Clearly, the Zodiac must have known that offering just five different symbols in a code of nine is open to many different interpretations, and hence practically unsolvable. Therefore, one could suggest this wasn't his intention- he was simply teasing us with the mechanics of how the 340 cipher was designed, by using a rudimentary diagram based on the Tim Holt comic- and something he would expand upon nearly a year later.
One can see how he uses the Zodiac symbol around the crosshairs in the December 16th 1969 'Fairfield' letter code, implying a uniformity of message, but aligns five symbols as an introduction to this design. This marries perfectly with 'Death By Gun', 'Death By Knife', 'Death By Fire' and 'Death By Rope.' Death is the introduction, following by the methods of death around the crosshairs. This is exactly what he offered us on October 27th 1970, when he placed the methods of death in the four quadrants of the bisecting Paradice and Slaves.  Here is a representation. 

Another Fairfield letter was mailed prior to this correspondence on December 7th 1969, mailed to the San Francisco Chronicle. Was the Zodiac Killer highlighting pertinent sections of the 340 code in as little as one month after his November 8th 1969 'Dripping Pen' card and cipher, negating the idea he could resist the temptation of giving us clues to its design.
The final offering to the mechanics of the 340 cipher may have come with his final confirmed correspondence- that of the 'Exorcist' letter mailed to the San Francisco Chronicle on January 29th 1974. ​         

The symbols at the foot of the 'Exorcist' letter were rearranged by Kevin Robert Brooks to reveal the words "To Kill". The message would then read "If I do not see this note in your paper, I will do something nasty, which you know I'm capable of doing...To kill."  
This threatening message was very similar to the trinity of communications that began the Zodiac's letter writing campaign on July 31st 1969, where he stated "I want you to print this cipher on the front page of your paper. In this cipher is my idenity. If you do not print this cipher by the afternoon of Fry.1st of Aug 69, I will go on a kill ram-Page Fry. night. I will cruse around all weekend killing lone people in the night then move on to kill again, until I end up with a dozen people over the weekend."  
In both the 'Exorcist' letter and July 31st communications the author would threaten "to kill'- as he would in the decoded 408 cipher. This is not particularly unusual for a serial murderer, but linking the unarranged symbols on the 'Exorcist' letter to the 340 code may connect yet another communication to the design of the cipher.
Key features of the 'Halloween' card, '13 Symbol' cipher, Fairfield communications and 'Exorcist' letter can be found in the 340 cipher, suggesting the Zodiac Killer was constantly pushing us towards the design of the 340 puzzle.
The following presentation will show a perceived correlation of the 'Exorcist' letter symbols to the only corrected section of the 340 cipher.

​​In the image on the left I have moved the two symbols on the extreme left of the 'Exorcist' letter to the right side as shown, without altering their position on the vertical axis. Then I have turned the extreme right symbol on the 'Exorcist' letter 90 degrees clockwise to form the new arrangement, shown in the bottom left image. This can now be compared to certain characters on the fifth, sixth, seventh line of the 340 cipher. The area in the proximity of the corrected sixth line.
Five of the six characters on the 'Exorcist' letter now bear a noticeable similarity to this area of the 340 cipher.
Did the Zodiac Killer sit down to create a uniform and continuous message using a code key in the 340 cipher, just like the message contained within the 408 cipher? If so, then the above findings were all created accidentally and unintentionally by the killer.
He placed an intersecting symbol at the center of the 340 cipher (+ sign), with two dashes at the periphery of the center line, to create the illusion of intersecting crosshairs.
Paradice and Slaves (uniformly of 17 characters) was created as a viable possibility bisecting the 340 cipher along the X and Y axis, along with "RAD" and "LAV" on the intersection of the cipher. The word "BY" (horizontally) was present in all four quadrants of the cipher. The 'near Zodiac' allied with the correct spelling of Zodiac on the 20th line produced the symmetry of three circled 8's. Using the identical technique and placing half the alphabet alongside the '13 Symbol' cipher, yet again, perfect symmetry was observed.
The three circled 8's, along with the symbols either side, all carried forward from the second cipher to the third cipher, and the 'Exorcist' letter symbols aligned with the corrected sixth line of the 340 cipher. This of course all happened by chance and the Zodiac Killer knew nothing about it.  
This would indicate that the Zodiac Killer had deliberately placed Paradice and Slaves into the 340 cipher, to which he would give us a clue one year later. The machinations of the '13 Symbol' cipher were most likely constructed in the mind of the killer before November 8th 1969, as to create a continuity between the two ciphers. The idea therefore, that the author of all these communications could interweave these designs together and still create a rambling uniform message to co-exist alongside them within the 340 cipher, would probably be a step too far.
The idea of a killer who sat down one evening to write a rambling 340 character message, to which he enciphered using a code key, who would then accidentally and inadvertently create so many by-products in his cipher without his knowledge, seems rather fortuitous. The Zodiac seemingly couldn't resist showing us the workings of his great masterpiece, and would eventually tell us that the 340 code was "no cipher", by giving us a portion of its true design in the 'Halloween' card on October 27th 1970. However, it's far more fun chasing chasing a real cipher, that will long continue for another 50 years.      

Here we will revisit an article published by the San Francisco Examiner on October 22nd 1969, in which Professor D.C.B. Marsh, president of the American Cryptogram Association laid down a challenge to Zodiac. The words he chose to use in this article may be the bedrock to much of the subsequent Zodiac communications, beginning with the 340 cipher, mailed only seventeen days after the San Francisco Examiner article. Here are the crucial extracts from that article.
'Dr Marsh told the Examiner today: "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in the cipher to established cryptogram experts. He knows, to quote Edgar Allen Poe, that any cipher created by man can be solved by man. Zodiac has not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald. Zodiac has not done this, because to tell the complete truth in relation to his name-in cipher code-would lead to his capture. I invite Zodiac to send The American Cryptogram Association a cipher code, which will truly and honestly include his name." It is difficult to believe that Zodiac, an avid reader of the newspapers, could resist such a challenge, particularly as he had promised to reveal his identity in the 408 cipher two months earlier, but failed to do so.  

The key section to note in the challenge by Professor D.C.B. Marsh is: "I invite Zodiac to send The American Cryptogram Association a cipher code, which will truly and honestly include his name."
Seventeen days later, the Zodiac Killer duly obliged with the November 8th 1969 340 cipher. Could this cipher have included the killer's name, but not in the format envisaged by Professor D.C.B. Marsh?
In a previous article entitled 'Zodiac Admitted 340 Not a Real Cipher' we examined the idea that the 340 cipher was inextricably linked to the Zodiac's 'Halloween' card, mailed on October 27th 1970. One can notice that the word "By" is located in each of the four quadrants of the 340 cipher. The author of the cipher also placed the letters F and K adjacent to one another no less than seven times (situated in each quadrant). But of particular interest was the corrected section on the sixth line of the 340 cipher, where the author chose to scrub out a forward facing K and replace it with a backwards K, elevated above the blacked out section.
The Zodiac Killer was known for numerous spelling errors in his communications, so why was it seemingly imperative to correct this one mistake? Was this correction crucial to the interpretation of the cipher, or was he drawing our attention to the letters in this section of the cipher? Are the F and K characters the initials of the Zodiac Killer?
This observation carries little merit on its own, so to bolster any argument for the initials of the Zodiac Killer being present in the 340 cipher, we have to explore the rest of his communications, particularly from around the time of the 'Halloween' card, in which we suggested was his admission that the 340 was unfortunately "no cipher". 
Linking the 'Halloween' card and 340 cipher through a Tim Holt comic book and explaining to us that the solution was "sorry no cipher." left us with the possibility that the 340 cipher was just a collection of puzzles, in which may have contained his name. The Zodiac Killer "wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in the cipher to established cryptogram experts", but he may have given us the abridged version.
We now enter the crucial phase of Zodiac communications, from the '13 Hole' postcard mailed on October 5th 1970, to the 'Exorcist' letter mailed on January 29th 1974. This critical period of four consecutive communications, is probably key to understanding the message the Zodiac Killer was trying to push. That the 340 was "sorry no cipher."      

In the '13 Hole' postcard the Zodiac Killer stated "There are reports city police pig cops are closeing in on me. Fk I'm crackproof. What is the price tag now?"
This section of pasted letters was placed upside down. The question one should be asking is 'what is the purpose behind this'. If its significance had no relevance to the actual postcard, did it have relevance to another communication.
The wording "FK I'm crackproof" could indicate that the killer thought he was immune from capture, however, it could also be a reference to his 340 cipher once again. The word "crackproof" is something that is unable to be cracked.
The 340 cipher would certainly be impervious to cracking, and certainly resistant to the attempts of The American Cryptogram Association had the killer devised a cipher not of conventional understanding, of which Professor D.C.B. Marsh was hoping when he laid down the challenge. The F and K text being flipped on the '13 Hole' postcard reminds one of the flipped K (next to F) on the only corrected portion of the 340 cipher. If FK were the Zodiac Killer's initials, then he certainly could be declaring that he was crackproof. 
​Professor D.C.B. Marsh stated  "He knows, to quote Edgar Allen Poe, that any cipher created by man can be solved by man. Zodiac has not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald. Zodiac has not done this, because to tell the complete truth in relation to his name-in cipher code-would lead to his capture." However, the Zodiac Killer could give his name in the form of initials without any fear of revealing his identity, and without risking his immediate capture. This may have manifested itself when he mailed his following cipher on April 20th 1970, when he opened with the gambit "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is...."  The code placed underneath was likely an immediate rebuttal to this question. 

All he is probably doing, is stating "My name is FK," and once again telling us he is crackproof, just like the '13 Hole' postcard, which would be mailed five and a half months later. The phrase "FK I'm crackproof" fits perfectly in circular formation within the '13 Symbol' cipher- which itself contains a series of circled 8's. Structured in this fashion, the F and K yet again align, as does the K and M in both the cipher and phrase. 
Continuing with our four consecutive communications from October 5th 1970 onward, we now have the October 27th 1970 'Halloween' card promising to yet again reveal his name: "I feel it in my bones, You ache to know my name, And so I'll clue you in." Again we feel disappointed only to see the word "Boo" on the card inner- but we know the Zodiac Killer isn't going to make this a conventional and straightforward offering. He offers us the phrase "sorry no cipher," but can we find his name or initials within this communication. This is where it gets more difficult, nevertheless, we are aware that within the '13 Hole' postcard he reversed or flipped the text containing "FK I'm crackproof" and he flipped the K (next to the F) on the sixth line of the 340 cipher. So the obvious conclusion, is to look for flipped or reversed text within the 'Halloween' card.  

The only place that F and K exist within one word on the 'Halloween' card, is in the word "knife." either side of the reversed letter N.
If we flipped the reversed N back to its appropriate position, the F and K of "knife" would be reversed yet again.
Now let us turn our attention to the peculiar configuration at the foot of the card inner. It would be extremely satisfying for the 'Halloween' card to read "I feel it in my bones, You ache to know my name, And so I'll clue you in... FK,"- so that is what we will create, by manipulating this card to read whatever we want it to.
The strange symbol, reading it as true as possible, appears like a number 7, followed by four dots and the letter F.
7+4=11=K (followed by F).
Without further ado, we shall move on to the next confirmed Zodiac communication on March 13th 1971, in which the Zodiac stated "This is the Zodiac speaking. Like I have allways said, I am crack proof. If the Blue Meannies are evere going to catch me, they had best get off their fat asses + do something. Because the longer they fiddle + fart around, the more slaves I will collect for my after life. I do have to give them credit for stumbling across my riverside activity, but they are only finding the easy ones, there are a hell of a lot more down there. The reason I'm writing to the Times is this, They don't bury me on the back pages like some of the others."
You will notice that the Zodiac Killer refers to "crackproof" once again, parroting his October 5th 1970 communication five months earlier. However, he doesn't just state he is crackproof, he reminds us that he has always been telling us he is crackproof, and quite possibly we just haven't got the message.

Roll on the January 29th 1974 'Exorcist' letter, signed "yours truley," nearly three years later, giving us our final installment of FK contained within the array of symbols at the foot of the letter. 
On this occasion he mirrors the sixth line of the 340 cipher by elevating the K above the letter F, and to its left. In fact, five characters from the Exorcist letter can be found in and around the corrected sixth line of the 340 cipher, as shown here in a previous article. This was possibly the fourth consecutive communication inferring an FK link and the suggestion that the author was indeed "crackproof."  
Was this a persistent and deliberate attempt to be true to the challenge laid down by The American Cryptogram Association and Professor D.C.B Marsh, by inserting his name (albeit initials) into the 340 cipher and subsequent communications, or just a case that my mind is F@@Ked after six exhausting years of looking for patterns where none exist.

The following observations are crafted with little, to no knowledge of cryptology, in respect to the validity or otherwise of the Zodiac 340 cipher. The cipher has withstood nearly 50 years of computer assaults, as well as some of the greatest minds in the field of codebreaking, yet as of writing, nothing has been officially verified as a solution despite many claims to the contrary.
The criteria for a definitive solution to the 340 cipher, is not when one person or few believe a solution has been achieved, it is when there is overwhelming consensus across the board, removing subjectivity from the equation.   
If the 340 cipher doesn't actually contain a message, it will never be broken, and paradoxically will remain unsolved despite no solution being possible. Having examined this cipher innumerable times, the only solution I can come to- is it has no solution.
This revolves around two key issues: In that, the Zodiac Killer may have had 'cipher three' formulated or drafted before he designed 'cipher two', to enable the interconnectivity between both. He had to think forwards to create backwards.
If we assume the 340 cipher has a solution and therefore a key (no matter how complex), then one may assume the Zodiac created the key, then created the message, and then applied the message to the key, so as to encrypt it. If this were the case, we must believe that the 'near Zodiac' that emerged on line 20 was by sheer chance. We would also have to believe, that had he crafted 'cipher three' completely independent of 'cipher two', with no intention of connecting both, then the following observations also happened completely by chance.     

Although covered many times before, the following will help explain the conundrum. 
Because the '13 Symbol' cipher was thirteen characters in total (half the alphabet) and began with an A and ended with an M, it was considered that by placing the first half of the alphabet alongside the '13 Symbol' cipher and numerically counting the difference between the columns, something may emerge. It did.
For example: C to N produces a difference of 11, whereas B and E produces a difference of 3. Non alphabetical symbols cannot produce a difference, so a zero is inserted. The resulting numbers produced have been color coded. The red section is before the first circled 8, the green section is after the last circled 8 and the blue section spans the first and last circled 8. Notice the perfect symmetry. The red and green numbers are identical read forwards or backwards, and the blue numbers again read identically in either direction, producing a mirror image.
An equally symmetrical pattern was created using the identical technique, when placing the correct spelling of Zodiac alongside the 'near Zodiac' on line 20 of the 340 cipher. 
Furthermore, the three 0's and three 8's created, can be combined and carried forward onto his '13 Symbol' cipher, which seemingly is what he did.
It is also apparent on the '13 Symbol' cipher, that either side of the three circled 8's are the Zodiac crosshairs and an inverted Aries symbol, apparent either side of the 'near Zodiac' on the final line of the 340 Cipher. So, the author has effectively carried eight symbols from one cipher to another.
The point being, that when the Zodiac Killer sat down at his desk and began to create a unique key for his 340 cipher, into which he was to place his message, it accidentally created the 'near Zodiac' on the 20th line, accidentally created the correlation between 'near Zodiac' and Zodiac to produce three circled 8's, accidentally created the symbols either side of 'near Zodiac,' that fully or in part, carried forward to the '13 Symbol' cipher in the correct position, and accidentally created symmetry in both instances. Or, the Zodiac crafted the '13 Symbol' cipher before the 340 cipher, which I would argue nobody believes.
The Zodiac Killer may have began his 340 cipher key from the bottom first, deliberately allocating specific letters in his message to create the 'near Zodiac' characters and continuing from there. But, if the interconnectivity exists between the 340 cipher and '13 Symbol' cipher, he effectively began with 'cipher three' first and worked backwards. However, this doesn't seem the likeliest of answers. The alternative, one could argue, is that the 340 contains only his pseudonym and nothing more.

The Zodiac may have presented us with a fictitious negro male on August 4th 1969, who by inference, provided us with some valuable information about the Zodiac Killer driving his brown car by the payphone at Springs and Tuolumne. Was this a red herring of a clue, much like the correction on line 6 of the 340 cipher.
It can be clearly seen on the left, that the Zodiac Killer was conscientious enough to correct an alphabetical K to a reversed K on line 6, even though spelling correctly was never much of an issue with the Zodiac Killer. To validate that this was a genuine mistake, he made sure that the original K had not been fully obscured. This may give the impression it is easy to mix up your K's when implementing your encrypted text. Or maybe this is what he wanted us to believe. Who in their right mind would correct a fake cipher? Therefore it must be genuine.
Did the Zodiac Killer implement this correction, conveniently leaving the blacked out character still visible (and just reversing it), to give us the impression that the 340 cipher is undeniably genuine. Was this move just another red herring, to again validate something that never was. 
Alternatively, the final line of the 340 cipher may contain just a part message, yet incomplete, bearing in mind that many believe the '13 Symbol' cipher may contain some form of a name. The 340 cipher may end with: "the Zodiac is".... to be continued on the next cipher. The anticipation of the newspapers and readers alike, for the sequel to be released, would be a Zodiac dream.

The following will provide an alternative to an earlier article 'The Lake Berryessa Greeting Card,' regarding the inspiration of the 340 character cipher and the two week period it was designed by the Zodiac Killer. 
On October 22nd 1969 Will Stevens wrote an article for the San Francisco Examiner entitled 'Cipher Expert Dares Zodiac to Tell Name.' Dr D.C.B. Marsh, president of the American Cryptogram Association challenged Zodiac to reveal his name by creating a cipher for them to crack. He stated "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in a cipher to established cryptogram experts. "Zodiac" had not done this, Marsh suggested, because to tell the complete truth in relation to his name, in cipher code, would lead to his capture. I invite 'Zodiac' to send The American Cryptogram Association a cipher code-however complicated."
​Michael Cole authored an excellent article detailing how Zodiac would take up this challenge exactly six months later, when he mailed the '13 Symbol' cipher to the newspapers, beginning with the line "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is...."
However, we will slightly deviate from the Michael Cole article by suggesting that both the 340 character cipher and '13 Symbol' cipher were responses initiated by the challenge of Dr D.C.B. Marsh. He issued the challenge- however complicated- and Zodiac would certainly oblige with his most complex cipher of all, just 17 days later. The Zodiac Killer, knowing he was dealing with cryptogram experts such as  Dr D.C.B. Marsh, professor of mathematics at the Colorado School of Mines in Golden, would certainly not disappoint, mailing the 340 character cipher just over two weeks later. He would then follow up on April 20th 1970 with a smaller code, implying he was now prepared to reveal his name.  

In his first correspondence to the newspapers the Zodiac Killer promised that the 408 cipher would contain his name, by stating "In this cipher is my idenity." This notion would soon be quashed, when the three-part cipher was cracked by Donald Gene and Bettye June Harden of Salinas, California, in a matter of days.
But this challenge on October 22nd 1969 was laid down by cryptogram experts, and probably the reason the Zodiac Killer went to the extreme, creating a cipher that remains unbroken nearly half a century later. Dr D.C.B. Marsh​ stated "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in a cipher." But the Zodiac wasn't going to play ball that easily, yet he did likely answer this challenge directly on the final line of the 340 character cipher by revealing his name in part. He placed the 'near Zodiac' from character 333 to 338. 
In the 408 cipher, the final section of the decoded message read "I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife." The '13 Symbol' cipher opened with the line "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is...."
Therefore, this should give us a clue to how the Zodiac Killer constructed the final two lines of the 340 character cipher, bearing in mind it was a response to the challenge proffered by Dr D.C.B. Marsh, and in part, revealed his pseudonym Zodiac. 
Here is one example of how the Zodiac may have signed off the 340 cipher, when you consider there are only two symbols after the 'near Zodiac,' in positions 339 and 340. There cannot be many reasonable options to consider for a two letter word.  

There are of course alternatives, such as "I will soon tell you who the Zodiac is," "My next cipher will reveal who the Zodiac is" or "The day will come when you'll know who Zodiac is." There are a myriad of possibilities, but always with the final two words being "Zodiac is." 
If the Zodiac began the 340 character cipher top down, are we to believe the 'near Zodiac' fell out by chance, and was not created specifically as a response to the American Cryptogram Association to reveal his name. The cipher may have signed off with something similar to the wording above, but could have been created from the bottom up, so as to lead us into his next cipher on April 20th 1970. The 408 cipher stated "I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife." The Zodiac Killer was then laid down a challenge on October 22nd 1969, and we know his propensity to reply to individuals when challenged. Seventeen days later, a cipher arrived at the San Francisco Chronicle. Can this be a coincidence such a short time after the challenge by Dr D.C.B. Marsh? He signs off the 340 character cipher, now promising he will soon reveal who the Zodiac is. Then 5 months later he seemingly is true to his promise, stating "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is...."
The second and third ciphers may be linked by the name Zodiac and a simple trick of mathematics, shown here. 
​           

Did the fact that Dr D.C.B. Marsh, being a professor of mathematics, play any part in this possible numerical solution, or the Zodiac Killer's  circled three eights (if indeed that is what they were). The killer would later state in the April 20th 1970 letter "PS I hope you have fun trying to figgure out who I killed."​​​   
Dr Marsh told the Examiner "That first code was complicated... and the maker obviously knew what he was doing. But it never included the true identity of Zodiac." But can we be sure the Zodiac read this article and responded from his basement residence.
Look at the accompanying news article to the Dr D.C.B. Marsh article, entitled  "Tunisia Hit by Heavy Rains." It reads "New torrential rains pounded Tunisia all last night and today, nearly isolating Tunis and Bezerte from the rest of the country. Broadcasts warned residents of low-lying suburbs to head for higher ground. Basements filled, and some ancient buildings in the Medina showed signs of crumbling."
The Zodiac Killer replied in the April 20th 1970 offering, by stating
"I have killed ten people to date. It would have been a lot more except that my bus bomb was a dud.  I was swamped out by the rain we had a while back." This however, is most likely too cryptic even for Zodiac. 
But the fact remains, that Dr D.C.B. Marsh set the Zodiac Killer a challenge, and a little over two weeks later he responded with an even more "complicated" cipher than the 408, possibly promising the professor of mathematics a solution to his identity in due course. One that arrived on April 20th 1970- but whether it held true to the promise of his name is another matter.​ 

Michael Cole- http://zodiacrevisited.com/name-cipher-motivation

The following will again be a little bit of mathematical trickery regarding the 'Halloween', '13 Hole' and 'Pines' cards- placing the number 888 (Jesus) alongside each and every one.  From the 408 cipher split into three lines of 8, the 'near Zodiac' on the 20th line of the 340 forming 888, the three 8's on the '13 Symbol' cipher, coupled with the same code being used to find 444 in the final two ciphers, we will now move on to the final three cryptic cards in the Zodiac repertoire. To understand this presentation, it is important to read two previous articles 'The Bible Code of a Killer' and '340 Cipher-Embedded Symmetry'.  However, it must be stressed that this is not claiming a definitive solve to the Zodiac mystery and must be viewed with a health warning.

​In every correspondence mentioned above, it was claimed the Zodiac was attempting to place his name alongside the name of Jesus, the savior of souls for the afterlife: "All the (people) I have killed will become my slaves. I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife." He wouldn't give us his name, but he may have given us Jesus. Here is the next cryptic correspondence with two unusual features, using the identical code employed to find 444 in both the final two canonical ciphers. The Zodiac again places his name alongside Jesus in the form of a messiah complex (also known as the Christ complex or savior complex).
Using the Zodiac code above, it was applied to the '13 Hole' postcard below, giving out the figures 43+120+347+36+342 = 888.
Jesus, the savior of souls, is now firmly alongside the Zodiac Killer once again. You will notice that the number 13 has been converted to one and three. This is done to transfer it into text form (to enter into the Zodiac code), exactly the same technique employed in the two previous ciphers, where the Omega, Taurus and Aries symbols were also converted into text form.
If we had left the figure 13 alone, that line would have totaled 360 (the degrees in a circle). Giving us 13 and 360 (13 punch holes). 

The next correspondence was the 'Halloween' card mailed on October 27th 1970. But this marked a deviation in the Zodiac's thinking. He was now likely trying to simplify things in an effort to push us towards Jesus- Hallelujah.
In the flap of the envelope he writes "sorry no cipher" twice, in the form of a multiplication sign. He could easily have written  "sorry no cipher" once, but evidently wanted to form the multiplication sign as an offering to our savior. If there was no cipher, then there is no code. The only 'cipher-like code' on the 'Halloween' card is the configuration of letters (not dissimilar to the "sorry no cipher" offering). The Zodiac intersected Paradice and Slaves, with four quadrants containing the words By Fire, By Gun, By Rope and By Knife. Was the word By a form of multiplication.
       

Using the path of least resistance we added up the letters in the 'cipher-like code', which totaled 37, and multiplied it by "sorry no cipher", placing it over the cross of Paradice and Slaves, as both formed a similar design. There are 24 letters in the four quadrants, giving us 37 X 24 = 888.
There were 37 letters in the 'cipher-like code' and we needed a number to multiply it by. In this case 24.
The next postcard was the 'Pines card' mailed on March 22nd 1971. If the Zodiac was simplifying matters, then this card would follow the identical technique displayed in the 'Halloween' card.
The 'Pines' card offered a set of 5 phrases.[1] 'Sierra Club'  [2] 'Sought Victim [3] 'Peek through the pines' [4] 'pass Lake Tahoe areas'  [5] 'around in the snow.'
The letters on this card would add up to exactly double the amount on the 'Halloween' card- exactly 74. 
We again needed a number to multiply it by. So let us take a punt on the figure 12 which the Zodiac supplied. 
​74 X 12 = 888 once again.  

But would the old Zodiac code resurface in one final offering on the 'Pines' card front- pushing us in both directions. 
The Zodiac drew our attention to Paul averly=chronicle.
Using the Zodiac code at the top of this page:
PAUL AVERLY = 3162 155522 = 32
CHRONICLE = 365215325 = 32
Thereby giving us PAUL AVERLY=CHRONICLE.

This completes the 888 and 444 sequence through seven cryptic Zodiac communications. But whether it is really there, or just a case of mathematical trickery and wordplay, is something only Zodiac knows.
Maybe the afterlife holds all the answers.

THE BIBLE CODE OF A KILLER

The Zodiac created four ciphers, of which only one has ever been solved and confirmed by overwhelming consensus. 
The third code is simply too short to achieve any meaningful decryption and the 'Button' letter '32 Symbol' code has only three repeating characters, making these two codes, without a key, effectively unbreakable. If we had the key however, then we would be back in business.
​It is perfectly reasonable after the solve by Donald Gene and Bettye June Harden in the August of 1969, to believe that all the remaining ciphers contain a message, after all, what would be the point of them other than a joke on Zodiac's part.
​It is my contention that the remaining three ciphers are all probably linked by religion, and Jesus Christ in particular.
The Zodiac chose a Celtic Cross style moniker, talked of "paradice" and the "afterlife," and placed crucifix style designs in his 'Halloween' and '13 Hole' postcards. You could say the Zodiac Code was the forerunner to the Da Vinci Code.
The key to the Zodiac Code is the previously discussed '13 Symbol' cipher, where the Zodiac splits the alphabet A through M to expose perfect symmetry in the third cipher. This is the template we shall use in the '13 Symbol' and '32 Symbol' ciphers, and in both instances arrive at exactly the same holy number. 
The Zodiac crosshairs can be noted in every cipher or code, so it is imperative we derive a mathematical figure for this moniker. But first we shall present the Zodiac Code that will be used on both ciphers.

The alphabet on the right has been split symmetrically into two halves. A through M was used in the Embedded Symmetry article, in which only the numbers 3, 1 and 5 were ever generated. The number 315 can be generated in several ways using the Zodiac Killer communications, but the simplest way is to take the Zodiac horoscope.
The Zodiac used what appeared to be an upside-down Aries symbol on the April 20th 1970  '13 Symbol' cipher. Many people also considered that the three circled 8's were in fact three circled Taurus symbols. But the reason the Zodiac Killer circled them, was possibly so they could be interpreted as both. Since we are dealing with the Zodiac horoscope, we will take the characters as one Aries and three Taurus symbols.

On the left is the Zodiac horoscope placed into the Zodiac Code (above).
This generates the figure 315 for the Zodiac crosshairs. 
Because we will be using Aries and Taurus in the '13 Symbol' cipher, I will explain how to arrive at the figures in brackets:
ARIES = A+R+I+E+S = 1+5+5+5+6 = 22.  
TAURUS = T+A+U+R+U+S = 7+1+6+5+6+6 =31.
ARIES =22, TAURUS = 31.

Before we move on it is important to mention the following again.
'In Christian numerology, the number 888 represents Jesus, or sometimes more specifically Christ the Redeemer. This representation may be justified either through gematria, by counting the letter values of the Greek transliteration of Jesus' name, or as an opposing value to 666, the number of the beast. Wikipedia.
In English gematria the figure for Jesus is 444'.  
If the Zodiac was creating his own bible code and referencing the rebirth of Christ using the number 8 for infinity, one would hope to find the figure 444 in the '13 Symbol' cipher shown below.  
​
Let us proceed and place the numbers alongside the relevant characters (see below). 
Notice again how the alphabetical characters only produce the figures 3, 1 and 5, as does the figure 315 representing the Zodiac crosshairs. 
The total value of the '13 Symbol' cipher is 444, representing Jesus. 

​We shall now move on to the '32 Symbol' cipher mailed just two months after the previous cipher. It contained only three repeating characters, the letter C, the letter O and the clear triangle, making it impossible to solve without a recognized key.
This led me to believe that these two ciphers were only solvable by some form of mathematical key.
Below I have used the same technique, using the Zodiac Code, representing the letters of the '32 Symbol' cipher by numbers. The Zodiac crosshairs are again attributed the 315 value and the Aries symbol the figure 22 once more. This time however, we have an Omega symbol, so we have to attribute it a figure.
OMEGA = O+M+E+G+A = 2+1+5+7+1 = 16. The six geometric shapes in the '32 Symbol' cipher cannot be attributed a name, and therefore cannot be attributed a value. They have been marked with a red X. 
You can see below, that when the numerical values are added up we arrive at the figure 444 once again.
Zodiac representing the figure 888, and both the remaining ciphers totaling 888. Whether it be 444 or 888, the reference to Jesus or Jesus Christ through the bible code of the Zodiac Killer is certainly possible. 

​The '408' cipher was divided up into three parts and mailed to the San Francisco Chronicle, Vallejo Times-Herald and San Francisco Examiner newspapers, but the final 18 characters of this cipher were unable to be decoded. Many speculated as to whether this was just filler to create three equal parts of 8 lines. Was this the rudimentary beginnings of 888, that he would carry through to his remaining ciphers and the name Zodiac itself? 

340 CIPHER- EMBEDDED SYMMETRY

This is a rehash of earlier articles concerning the 340 cipher and 13 Symbol cipher, regarding their symmetry and correlation to one another. If you are familiar with the 888 theory, then you need go no further.
The 340 cipher was the second cipher mailed on November 8th 1969- the 13 symbol cipher was the third cipher mailed on April 20th 1970, separated by just over five months. The Zodiac would refer to his 340 cipher at the beginning of the April 20th letter, stating: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is...."
This could be a simple clue leading into his new cipher, however, the author of the letter is highly unlikely to submit his real name. In addition, it is simply too short a code to be verifiable, and the Zodiac Killer must surely have known this if he had any rudimentary knowledge of code breaking. But with a clue or key affixed to the 13 symbol code, then we may have a chance.
Up to this point in time we only knew the murderer by the pseudonym Zodiac, so let us complete the introduction on the April 20th 1970 letter: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is Zodiac."  This however sounds a little flawed, so it is imperative we replace Zodiac with an alternative, something possibly embedded within the name Zodiac itself. 

​The 340 cipher has been entered into every powerful computer known to man with no solution being found, leading many people to believe it has no solution at all, and is in effect total 'gibberish.'  I don't know about the entirety of the 340 cipher, but the final twentieth line of the cipher does contain perfect symmetry in six of the final eight characters. In addition eight of the final nine characters are effectively carried forward from the 340 cipher to the 13 Symbol cipher, linking cipher two and cipher three together. In the 13 Symbol cipher he did refer to "My name is..," so we will look for his pseudonym in the 340 cipher and take this as the clue. 
We already know that six symbols on the twentieth line of the 340 cipher look very similar to his pseudonym Zodiac, but was this unintentional or deliberate. To find this out we shall look at the symmetry of both ciphers.
The 13 symbol cipher from a character standpoint is extremely organized. It starts and ends with three alphabetical characters. The three circled 8's are symmetrically placed in positions 5, 7 and 9. The Zodiac symbol and 'upside down Aries' symbol are four in from either side. Either the Zodiac just happened upon this symmetry, or he designed it for purpose.
Bearing this symmetry in mind, we will look for a symmetrical answer in both the 340 cipher and 13 Symbol cipher, and in addition symmetry between the two.
The Zodiac Killer was undoubtedly an egotist, so it wouldn't be all that surprising if he used his own pseudonym in the clue, and embedded the answer within the name Zodiac. In the following examination I will be using the identical mathematical technique on both the 340 cipher and 13 Symbol cipher, to show perfect symmetry in both instances. It was this egotism that led me to believe the clue resided in the 'near' Zodiac on the twentieth line of the 340 cipher. So using a comparison technique, I placed the proper spelling of Zodiac under the 'near' Zodiac and simply counted the numerical alphabetical difference in the columns. But first let us take a look at the 13 Symbol cipher and note the bottom two lines in the diagram below.
Because of not only the existing symmetry within this cipher, but the fact it was thirteen characters in length, began with an A and ended with an M, along with Zodiac's penchant for word games, it seemed the obvious choice to place the first 13 letters of the alphabet under the cipher. 
A to A = 0, B to E = 3, C to N = 11, F to K = 5, H to M = 5, K to N = 3, A to L = 11. 
It is achieved by staying within the alphabet and counting the numerical distance between the letters. Obviously, when we do not have two alphabetical characters there can be no difference, so a zero is attributed. You could attribute an X, it actually makes no difference to the resulting symmetry.

​Highlighted in red and green the obvious symmetry can be observed. But how likely can this be created by accident. 
By taking the three circled 8's as H's, it can still be seen that only three natural numbers are ever produced - 3, 1 and 5. 
How do we know if this is the technique that Zodiac employed? If we apply this technique to the 'near' Zodiac on the twentieth line of the 340 cipher using the correct spelling of Zodiac and it again produces perfect symmetry, then we have possibly bolstered our case. If, in addition, it produces something significant that relates to the 13 Symbol cipher, does it then become even more compelling? The most obvious choice this time is to place Zodiac underneath the six symbols on the twentieth line, like so:

Using the identical technique we used in the 13 Symbol cipher, we shall again count the numerical difference in the columns.
Z to Z = 0, O to O = 0, D to triangle = 0, I to A = 8, A to I = 8, C to K = 8.
That is three 0's and three 8's, carried forward to the 13 Symbol cipher on April 20th 1970. But that is not all.
Either side of the 'near' Zodiac on the twentieth line of the 340 cipher we have the crosshairs and an 'inverted Aries' in part.  
Both of which are situated on the 13 Symbol cipher, either side of the circled 8's (shown in the red rectangular boxes above).
This means, that effectively eight characters out of the last nine were effectively carried forward from the 340 cipher to the 13 symbol cipher. It could be argued that the last eight characters of the 340 cipher were carried forward, the plus sign (+) at the end of the 340 cipher signifying their addition to the 13 Symbol cipher.
​Zodiac is now represented by the three circled 8's. 'In Christian numerology, the number 888 represents Jesus, or sometimes more specifically Christ the Redeemer. This representation may be justified either through gematria, by counting the letter values of the Greek transliteration of Jesus' name, or as an opposing value to 666, the number of the beast.' Wikipedia. This may be important when we consider the Zodiac's tendency to speak of "paradise" and the "afterlife" in many of his communications, in particular his 408 cipher. He would also cross "paradice" and "slaves" in the form of a crucifix on the Halloween card, as well as pasting a red crucifix on the 13 Hole postcard.  
You can see in the above diagram that the letters K and M are embedded within the three 8's and therefore embedded in the name Zodiac. Were these his initials, and was he elevating himself to divine status? He certainly had the ego for it.

# There are some additional features of interest:
The 408 cipher was divided up into three sections of 8 lines and mailed to three different newspapers.
The final line of the 408 cipher contains an M and reversed K.
The final line of the 340 cipher contains an M and reversed K.
The 13 Symbol cipher contains the letter M and K.
The final character at the end of each of the three communications of the 408 cipher is either an M or reversed K.
The top line of the 32 Symbol cipher mailed on June 26th 1970 contains an M and reversed K.

This website contains no advertisements. To help keep it running, any donations, however small, would be greatly appreciated. Thank you. Richard. ​

The Zodiac created four ciphers, of which only one has ever been solved and confirmed by overwhelming consensus. 
The third code is simply too short to achieve any meaningful decryption and the 'Button' letter '32 Symbol' code has only three repeating characters, making these two codes, without a key, effectively unbreakable. If we had the key however, then we would be back in business.
​It is perfectly reasonable after the solve by Donald Gene and Bettye June Harden in the August of 1969, to believe that all the remaining ciphers contain a message, after all, what would be the point of them other than a joke on Zodiac's part.
​It is my contention that the remaining three ciphers are all probably linked by religion, and Jesus Christ in particular.
The Zodiac chose a Celtic Cross style moniker, talked of "paradice" and the "afterlife," and placed crucifix style designs in his 'Halloween' and '13 Hole' postcards. You could say the Zodiac Code was the forerunner to the Da Vinci Code.
The key to the Zodiac Code is the previously discussed '13 Symbol' cipher, where the Zodiac splits the alphabet A through M to expose perfect symmetry in the third cipher. This is the template we shall use in the '13 Symbol' and '32 Symbol' ciphers, and in both instances arrive at exactly the same holy number. 
The Zodiac crosshairs can be noted in every cipher or code, so it is imperative we derive a mathematical figure for this moniker. But first we shall present the Zodiac Code that will be used on both ciphers.    

The alphabet on the right has been split symmetrically into two halves. A through M was used in the Embedded Symmetry article, in which only the numbers 3, 1 and 5 were ever generated. The number 315 can be generated in several ways using the Zodiac Killer communications, but the simplest way is to take the Zodiac horoscope.
The Zodiac used what appeared to be an upside-down Aries symbol on the April 20th 1970  '13 Symbol' cipher. Many people also considered that the three circled 8's were in fact three circled Taurus symbols. But the reason the Zodiac Killer circled them, was possibly so they could be interpreted as both. Since we are dealing with the Zodiac horoscope, we will take the characters as one Aries and three Taurus symbols. 

On the left is the Zodiac horoscope placed into the Zodiac Code (above).
This generates the figure 315 for the Zodiac crosshairs. 
Because we will be using Aries and Taurus in the '13 Symbol' cipher, I will explain how to arrive at the figures in brackets:
ARIES = A+R+I+E+S = 1+5+5+5+6 = 22.  
TAURUS = T+A+U+R+U+S = 7+1+6+5+6+6 =31.
ARIES =22, TAURUS = 31.

Before we move on it is important to mention the following again.
'In Christian numerology, the number 888 represents Jesus, or sometimes more specifically Christ the Redeemer. This representation may be justified either through gematria, by counting the letter values of the Greek transliteration of Jesus' name, or as an opposing value to 666, the number of the beast. Wikipedia.
In English gematria the figure for Jesus is 444'.  
If the Zodiac was creating his own bible code and referencing the rebirth of Christ using the number 8 for infinity, one would hope to find the figure 444 in the '13 Symbol' cipher shown below.  
​
Let us proceed and place the numbers alongside the relevant characters (see below). 
Notice again how the alphabetical characters only produce the figures 3, 1 and 5, as does the figure 315 representing the Zodiac crosshairs. 
The total value of the '13 Symbol' cipher is 444, representing Jesus. 

We shall now move on to the '32 Symbol' cipher mailed just two months after the previous cipher. It contained only three repeating characters, the letter C, the letter O and the clear triangle, making it impossible to solve without a recognized key.
This led me to believe that these two ciphers were only solvable by some form of mathematical key.
Below I have used the same technique, using the Zodiac Code, representing the letters of the '32 Symbol' cipher by numbers. The Zodiac crosshairs are again attributed the 315 value and the Aries symbol the figure 22 once more. This time however, we have an Omega symbol, so we have to attribute it a figure.
OMEGA = O+M+E+G+A = 2+1+5+7+1 = 16. The six geometric shapes in the '32 Symbol' cipher cannot be attributed a name, and therefore cannot be attributed a value. They have been marked with a red X. 
You can see below, that when the numerical values are added up we arrive at the figure 444 once again.
Zodiac representing the figure 888, and both the remaining ciphers totaling 888. Whether it be 444 or 888, the reference to Jesus or Jesus Christ through the bible code of the Zodiac Killer is certainly possible. 

The '408' cipher was divided up into three parts and mailed to the San Francisco Chronicle, Vallejo Times-Herald and San Francisco Examiner newspapers, but the final 18 characters of this cipher were unable to be decoded. Many speculated as to whether this was just filler to create three equal parts of 8 lines. Was this the rudimentary beginnings of 888, that he would carry through to his remaining ciphers and the name Zodiac itself ? 

http://www.zodiacciphers.com/zodiac-news/340-cipher-embedded-symmetry   

This is a rehash of earlier articles concerning the 340 cipher and 13 Symbol cipher, regarding their symmetry and correlation to one another. If you are familiar with the 888 theory, then you need go no further.
The 340 cipher was the second cipher mailed on November 8th 1969- the 13 symbol cipher was the third cipher mailed on April 20th 1970, separated by just over five months. The Zodiac would refer to his 340 cipher at the beginning of the April 20th letter, stating: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is...."
This could be a simple clue leading into his new cipher, however, the author of the letter is highly unlikely to submit his real name. In addition, it is simply too short a code to be verifiable, and the Zodiac Killer must surely have known this if he had any rudimentary knowledge of code breaking. But with a clue or key affixed to the 13 symbol code, then we may have a chance.
Up to this point in time we only knew the murderer by the pseudonym Zodiac, so let us complete the introduction on the April 20th 1970 letter: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is Zodiac."  This however sounds a little flawed, so it is imperative we replace Zodiac with an alternative, something possibly embedded within the name Zodiac itself. 

​The 340 cipher has been entered into every powerful computer known to man with no solution being found, leading many people to believe it has no solution at all, and is in effect total 'gibberish.'  I don't know about the entirety of the 340 cipher, but the final twentieth line of the cipher does contain perfect symmetry in six of the final eight characters. In addition eight of the final nine characters are effectively carried forward from the 340 cipher to the 13 Symbol cipher, linking cipher two and cipher three together. In the 13 Symbol cipher he did refer to "My name is..," so we will look for his pseudonym in the 340 cipher and take this as the clue. 
We already know that six symbols on the twentieth line of the 340 cipher look very similar to his pseudonym Zodiac, but was this unintentional or deliberate. To find this out we shall look at the symmetry of both ciphers.
The 13 symbol cipher from a character standpoint is extremely organized. It starts and ends with three alphabetical characters. The three circled 8's are symmetrically placed in positions 5, 7 and 9. The Zodiac symbol and 'upside down Aries' symbol are four in from either side. Either the Zodiac just happened upon this symmetry, or he designed it for purpose.
Bearing this symmetry in mind, we will look for a symmetrical answer in both the 340 cipher and 13 Symbol cipher, and in addition symmetry between the two.
The Zodiac Killer was undoubtedly an egotist, so it wouldn't be all that surprising if he used his own pseudonym in the clue, and embedded the answer within the name Zodiac. In the following examination I will be using the identical mathematical technique on both the 340 cipher and 13 Symbol cipher, to show perfect symmetry in both instances. It was this egotism that led me to believe the clue resided in the 'near' Zodiac on the twentieth line of the 340 cipher. So using a comparison technique, I placed the proper spelling of Zodiac under the 'near' Zodiac and simply counted the numerical alphabetical difference in the columns. But first let us take a look at the 13 Symbol cipher and note the bottom two lines in the diagram below.
Because of not only the existing symmetry within this cipher, but the fact it was thirteen characters in length, began with an A and ended with an M, along with Zodiac's penchant for word games, it seemed the obvious choice to place the first 13 letters of the alphabet under the cipher. 
A to A = 0, B to E = 3, C to N = 11, F to K = 5, H to M = 5, K to N = 3, A to L = 11. 
It is achieved by staying within the alphabet and counting the numerical distance between the letters. Obviously, when we do not have two alphabetical characters there can be no difference, so a zero is attributed. You could attribute an X, it actually makes no difference to the resulting symmetry.    

Highlighted in red and green the obvious symmetry can be observed. But how likely can this be created by accident. 
By taking the three circled 8's as H's, it can still be seen that only three natural numbers are ever produced - 3, 1 and 5. 
How do we know if this is the technique that Zodiac employed? If we apply this technique to the 'near' Zodiac on the twentieth line of the 340 cipher using the correct spelling of Zodiac and it again produces perfect symmetry, then we have possibly bolstered our case. If, in addition, it produces something significant that relates to the 13 Symbol cipher, does it then become even more compelling? The most obvious choice this time is to place Zodiac underneath the six symbols on the twentieth line, like so:

Using the identical technique we used in the 13 Symbol cipher, we shall again count the numerical difference in the columns.
Z to Z = 0, O to O = 0, D to triangle = 0, I to A = 8, A to I = 8, C to K = 8.
That is three 0's and three 8's, carried forward to the 13 Symbol cipher on April 20th 1970. But that is not all.
Either side of the 'near' Zodiac on the twentieth line of the 340 cipher we have the crosshairs and an 'inverted Aries' in part.  
Both of which are situated on the 13 Symbol cipher, either side of the circled 8's (shown in the red rectangular boxes above).
This means, that effectively eight characters out of the last nine were effectively carried forward from the 340 cipher to the 13 symbol cipher. It could be argued that the last eight characters of the 340 cipher were carried forward, the plus sign (+) at the end of the 340 cipher signifying their addition to the 13 Symbol cipher.
​Zodiac is now represented by the three circled 8's. 'In Christian numerology, the number 888 represents Jesus, or sometimes more specifically Christ the Redeemer. This representation may be justified either through gematria, by counting the letter values of the Greek transliteration of Jesus' name, or as an opposing value to 666, the number of the beast.' Wikipedia. This may be important when we consider the Zodiac's tendency to speak of "paradise" and the "afterlife" in many of his communications, in particular his 408 cipher. He would also cross "paradice" and "slaves" in the form of a crucifix on the Halloween card, as well as pasting a red crucifix on the 13 Hole postcard.  
You can see in the above diagram that the letters K and M are embedded within the three 8's and therefore embedded in the name Zodiac. Were these his initials, and was he elevating himself to divine status? He certainly had the ego for it.

# There are some additional features of interest:
The 408 cipher was divided up into three sections of 8 lines and mailed to three different newspapers.
The final line of the 408 cipher contains an M and reversed K.
The final line of the 340 cipher contains an M and reversed K.
The 13 Symbol cipher contains the letter M and K.
The final character at the end of each of the three communications of the 408 cipher is either an M or reversed K.
The top line of the 32 Symbol cipher mailed on June 26th 1970 contains an M and reversed K.

Related article: http://www.zodiacciphers.com/zodiac-news/peek-through-the-pines
​

This website contains no advertisements. To help keep it running, any donations, however small, would be greatly appreciated. Thank you. Richard. ​

The Zodiac Killer teased us with his name on more than one occasion, firstly in the July 31st 1969 San Francisco Chronicle letter where he stated "I want you to print this cipher on the front page of your paper. In this cipher is my idenity." He would follow this up with the 'My Name is...' letter on April 20th 1970 and the 'Halloween' card on October 27th 1970 tempting us with his name again; "I feel it in my bones, You ache to know my name, And so I'll clue you in.." 
​It would appear however, this was never to be the case and we are still no nearer to securing the identity of the Zodiac Killer nearly half a century later. It always seemed strange the Zodiac Killer would interpose the Gilbert and Sullivan Mikado into his correspondence, leading researchers to believe he was a fan of the theater, having quoted three acts of The Mikado in the 'Little List' letter of July 26th 1970 and 'Exorcist' letter of January 29th 1974. But there may be an ulterior motive behind this apparent fascination with Gilbert and Sullivan, in that the killer was using the Mikado to reveal his name, and likely through four mailings rather than the accepted two. We will take a closer look at these four correspondences and the speculative links between them, without claiming this is anything more than coincidence. Let us first look at the 'Exorcist' letter.   

The first thing to notice is its carefully structured appearance, being divided neatly into four sections of text. The curious thing about the correspondence is Zodiac wrote "Signed, yours truley," as though he was about to offer up his name in the third block of writing. He then recited ​Act II -On a tree by a river from The Mikado. It seemed like Zodiac was wasting our time, plucking out random verses from The Mikado, that is until you read verse three of this particular act. It not only contained a reference to 'name', but pointed us towards 'The My Name is...' cipher, mailed on April 20th 1970. Here is verse three.
Now I feel just as sure as I'm sure that my name
Isn't Willow, titwillow, titwillow,
That 'twas blighted affection that made him exclaim
"Oh, willow, titwillow, titwillow!"
And if you remain callous and obdurate, I
Shall perish as he did, and you will know why,
Though I probably shall not exclaim as I die,
"Oh, willow, titwillow, titwillow!"

Was the Zodiac Killer giving us clues to his identity or name, by leading us back to the '13 Symbol' cipher. This observation on its own is meaningless, so we will travel back in time to the 'Little List' letter mailed on July 26th 1970, the supposed only other correspondence to contain references to The Mikado- in fact two. The first section of the 'Little List' letter pulled lines from  'A more humane Mikado', and continued on to extensively recite Gilbert and Sullivan's Mikado Act One Part 5a  'As some day it may happen', performed by Ko-Ko. In the introductory part of the letter, Zodiac simply boasted about how he would torture his slaves in paradise, but he again did something curious, by selecting just one small section of 'A more humane Mikado,' despite it being ten verses in length. The same as he did in the 'Exorcist' letter. He then continued to paraphrase the entirety of 'As some day it may happen'.
The 'Exorcist' letter, we have shown to have tenuous links to the April 20th 1970 'My Name is...' letter, using verse three of 'Tit-Willow'. So let us look at the small section of text Zodiac selected from 'A more humane Mikado.'
The 'Little List' letter read "And all billiard players I shall have them play in a darkened dungen cell with crooked cues + Twisted Shoes."  Why does Zodiac select this small portion. Was this also hinting towards the 'My Name is...' cipher.
When we think of billiard players or billiard balls from the standpoint of America, eight-ball comes to mind, and the circled eights on the '13 Symbol' cipher. 

This is the full verse (right) from 'A more humane Mikado.' It is actually verse eight out of ten, providing us with the numerical link, as did verse three from the 'Exorcist' letter. The Zodiac Killer did state on the 'My Name is...' letter; "PS I hope you have fun trying to figgure out who I killed."​​​
There is however another link from 'A more humane Mikado,' to the alphabetical characters on the '13 Symbol' code mailed by Zodiac.
The Zodiac Killer supplied us with eight alphabetical characters, reading from left to right  A, E, N, K, M, N, A and M.
In the diagram below, key sections of 'A more humane Mikado' are highlighted for comparison to the '13 Symbol' cipher. Seven letters have been highlighted in green and yellow. This is where we must take a bold leap of faith, and consider that the Zodiac Killer chose The Mikado by Gilbert and Sullivan because it simply contained his name, Kim. Nothing more theatrical than that. 

The green highlighted sections on 'A more humane Mikado' in reverse, read KIMNAM. If we believe therefore, that the middle eight represents the letter I on the '13 Symbol' cipher, it reads forward KIMNAM, exactly the same. The remaining letters of the cipher AEN are shown highlighted in yellow. Every letter on the '13 Symbol' cipher is contained within this section of seven letters. 
​The three eights encapsulated his identity, just like the three eights at the foot of the '340' character cipher mailed on November 8th 1969: The Mathematics of the 13 Symbol Cipher. Who said the Magic 8 ball was just for telling fortunes! Additionally, Mikado can be formed using the alphabetical characters on the 20th line of the '340' cipher.
The Zodiac was keen to share with us what he had in store for his slaves in paradise:
"This is the Zodiac speaking. Being that you will not wear some nice buttons, how about wearing some nasty buttons. Or any kind of buttons that you can think up. If you do not wear any type of buttons, I shall (on top of everything else) torture all 13 of my slaves that I have waiting for me in Paradice. Some I shall tie over ant hills and watch them scream + twich and squirm. Others shall have pine splinters driven under their nails + then burned. Others shall be placed in cages + fed salt beef untill they are gorged then I shall listen to their pleass for water and I shall laugh at them. Others will hang by their thumbs + burn in the sun then I will rub them down with deep heat to warm them up. Others I shall skin them alive + let them run around screaming. And all billiard players I shall have them play in a darkened dungen cell with crooked cues + Twisted Shoes. Yes I shall have great fun inflicting the most delicious of pain to my slaves."
The talk of slaves, paradise, pine splinters, dungeons and hanging his 'prisoners' by the thumbs, catapulted me to the 'Halloween' card mailed on October 27th 1970, and the last Mikado installment. The Zodiac Killer placed some wording around the knothole in the tree:"peek a boo you are doomed." Bearing in mind that The Mikado opened to the paying public on March 14th 1885, and was hugely successful, running for 672 performances at the Savoy Theatre in London, a British connection had to be sought. The British term for peek-a-boo is peep-bo, and peep-bo is a character in The Mikado.      

The following will not propose a solution to the '13 Symbol' cipher because the limited characters in the code make that simply impossible without a key, and the author of the letter must surely have known that, even if he had limited cipher experience. A search for the solution however, could be an unnecessary quest, as the Zodiac Killer may have given us the answer just five and a half months later. The Zodiac Killer vowed to give us his name in his earlier 408 cipher, only to renege on the promise. The idea therefore, that he would reveal his name in the April 20th 1970 correspondence is equally unlikely. But he may have given us something, useless in of itself from a standpoint of incrimination, on account of its brevity, but something nonetheless. 
The October 5th 1970 '13 Hole' postcard has links to the '13 Symbol' cipher for obvious reasons, but the author of the postcard does paste some unusual text, notably "Fk, I'm crackproof. What is the price tag now ?"   
Is there a correlation to the '13 Symbol' cipher?  Immediately after "Fk, I'm crackproof" the author asks about the price tag on his head. Immediately after the '13 Symbol' code on the April 20th 1970 correspondence the author writes "I am mildly cerous as to how much money you have on my head now."  So what is the likelihood "Fk, I'm crackproof" precedes this question also. It would make sense when the April 20th 1970 communication is read as a whole: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is FK, I'm crackproof." 
The phrase itself is 14 characters, so would be infinitely circular in configuration, beginning and ending with the letter F, like so. 

The letters K and M line up nicely in the code, nevertheless on its own it is pretty worthless.
Could the killer's initials be FK or KF, on account of the upside-down text on the '13 Hole' postcard, or could the killer simply want us to believe this is the case.
The FK in close proximity occurs seven times on the '340' cipher, but much more significantly, the eye is drawn to the 'mistake' on line six, where the author of the cipher elevates the letter K in reverse, next to the letter F. The author of the '13 Hole' postcard effectively rotates both letters through 180 degrees, again reversing the letter K. 
The 'Exorcist' letter mailed on January 29th 1974 looks somewhat similar to the sixth line of the '340' cipher, in that the strange symbolism at the foot of the letter appears to marry up. It contains what looks like a letter F, and to its elevated left is an upside-down K. But there is much more correlation, in that five of the characters on the 'Exorcist' letter bear a striking resemblance to five of the characters by the FK on the '340' cipher. http://www.zodiacciphers.com/zodiac-news/340-cipher-and-exorcist-link            

The elevated and reversed letter K, is positioned to the left of the letter F in both the '340' sixth line, and the 'Exorcist' letter symbolism. It is again reversed and positioned to the left of the letter F in "Fk, I'm crackproof" on the '13 Hole' postcard.
If the Zodiac Killer lived within a 10 minute walking radius of the Springs and Tuolumne payphone, then by examining land registry records in 1969 for males with FK or KF initials and cross checking their vital statistics, including photographs, would go a long way to deciding whether this is just another pattern, in a rich tapestry of Zodiac imaginings.

​http://www.zodiacciphers.com/zodiac-news/the-fictitious-negro-male