There is no definitive evidence to totally negate the idea that the 340 cipher contains a viable solution- with the mystery and allure of the Zodiac Killer code the driving force behind people wishing it were genuine. This, of course, exempts the 500+ people who have already solved the 340 cipher, in solutions now extending longer than the Bayeux Tapestry.  
Obviously, Zodiac researchers who specialize in the ciphers rather than the crimes themselves, have a vested interest in wishing the cipher to be a hidden message. This is the belief that keeps the dream alive.
But did the Zodiac Killer really have the ability to create a more difficult cipher than the 408, with a reasonable expectation of a solution. Placing 29 unique characters into a 32 symbol cipher, and creating a 13 symbol code would suggest not.
The October 22nd 1969 Examiner newspaper article by Will Stevens, 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. This may be the article that inspired the 340 cipher, and by association, the 'Halloween' card mailed approximately one year later.
 "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."
This contention is probably true- that the Zodiac Killer wouldn't reveal his name in any cipher (other than his pseudonym), and additionally, he likely used the fact "that any cipher created by man can be solved by man" as a springboard to create something extra special, other than a cipher. If we contend that the Zodiac Killer wrote his final letters in 1974, then is it likely that a killer touted as an attention seeker, could resist dropping us clues to the 340 cipher in his subsequent letters, spanning in excess of four years. 
Each and every one of his final three communications in late 1970 and early 1971 effectively told us he was crackproof. The upside down text on the October 5th 1970 'Pace' card stated "Fk I'm crackproof." The October 27th 1970 'Halloween' card proclaimed "sorry no cipher." The March 13th 1971 'Los Angeles' letter boasted "Like I have allways said, I am crack proof." But the Zodiac Killer hadn't always said he was crackproof- only in the two communications either side of the 'Halloween' card announcing "sorry no cipher." The suggestion he was crackproof, thereby not arising from his perceived ability to evade police, but from his smugness in knowing he created three ciphers he knew would never be solved. 

The Tim Holt comic find by Tahoe27 in 2013, and the recent assertion of a close alliance, not only with the 'Halloween' card, but the 340 cipher, has been covered here to reject the 340 cipher as containing a viable and coherent message.
In view of the "by knife" attribution on Bryan Hartnell's car door, it is arguable that the Zodiac Killer had the Tim Holt comic book or Rota Fortunae (Wheel of Death) in mind as he wrote on the car door. In other words, the concept predated the September 27th 1969 Lake Berryessa stabbings, rather than just the 'Halloween' card. The Lake Berryessa "by knife" attribution becoming the part inspiration for the complex puzzle of the 340 cipher.
The "by knife" method of death (on the right) is clearly the only one falling within its quadrant, as opposed to the others, which are all connecting with the central column.
This method of death was certainly prioritized by the Zodiac Killer, having placed it on Bryan Hartnell's vehicle (despite the fact the crime was obviously committed with a knife). The feasible presence of "by knife" within the 340 cipher. The possibility of a crude 'Halloween' card design in the December 16th 1969 'Fairfield' letter featuring "death by knife," along with the "Bleeding Knife of Zodiac" drawing. And finally, the 'October 27th 1970 'Halloween' card design and comic book, both containing "by knife" and mirroring the 340 cipher and 'Fairfield' letter.
Below are the speculative beginnings, attempting to interweave the '13 Hole' postcard into the emerging design. 

This is the last time this subject will be tackled for the foreseeable future, unless something magical sticks its head above the parapet- but before that happens- there is just one more addition to the idea of an extremely close alliance between the 'Halloween' card and 340 cipher, and the suggestion that the 340 cipher is not a meaningful and coherent message by the Zodiac Killer.
Just about every feature of the October 27th 1970 'Halloween' card, including the envelope and stamp, can be shown to exist within the 340 cipher, making the December 2013 discovery by Tahoe27, of a Tim Holt comic book connection, all the more compelling. Her discovery may have opened the door to finally end the debate on the validity of the 340 masterpiece, and place the pseudonym 'Zodiac' front and center to the 'Death Wheel' featured on the comic book cover.
At what juncture the Zodiac first stumbled across his pseudonym is of little importance, however, it could be argued that when he found it, he would likely research the name 'Zodiac' and use elements of his research to incorporate into his future correspondence. If he had happened upon the Tim Holt 'Death Wheel' comic prior to November 8th 1969, then the light bulb may have switched on, and his design of a crackproof cipher began in earnest. And possibly, a 340 cipher designed in tandem with the Tim Holt comic and cipher three, which he mailed just over five months later on April 20th 1970. His opening line of "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is....", he may have already known the answer to when he manufactured the illusion of a 340 character message.        

Here is a brief recap before we move on.
The 'Halloween' card stamp contained 17 letters "In the beginning God" that slotted nicely onto the first line of the 340 cipher, with characters 15,16 and 17 awkwardly similar- including the half-earth image present on the stamp.
Paradice and Slaves can be shown as a distinct possibility, bisecting the 340 cipher horizontally and vertically, just like the 'Halloween' card arrangement. Seventeen characters horizontally and vertically in either direction, to create the perfect crosshairs of Zodiac.
The word "by" can be found in all four quadrants of the 340 cipher, mirroring the 'Halloween' card arrangement.
At least seven, possibly eight characters on the 14th line of the 340 cipher can be formed into the design of the 'Halloween' card inner. Explanation here. 
"Sorry no cipher" written on the envelope inner and designed in similar fashion to Paradice and Slaves arrangement on both the 'Halloween' card and 340 cipher, explicitly instructed us that no cipher existed on November 8th 1969.
One has to presume that all these fell here by accident (including the inference to Zodiac on the 20th line), because to believe otherwise, would pour huge doubt on a Zodiac Killer who was able to simultaneously create a uniform message within the 340 cipher in conjunction with a 'bag of puzzles'. 
However, the Tim Holt 'Death Wheel' comic is not only interesting because it contains By Fire, By Gun, By Rope and By Knife, found in the 'Halloween' card, or because of "Redmask" or "Lady Doom," but because of the origin of the 'Death Wheel' or 'Wheel of Fortune' itself. 
Had the Zodiac Killer read anything about the pseudonym 'Zodiac' when he first appropriated it, then he may have known the relevance of the 'Wheel of Fortune' or 'Rota Fortunae,'. thereby triggering the inspiration for the 340 cipher, and the eventual 'Halloween' card explanation or solution to his devilish trick and treat.          

We could just assume that when the Zodiac Killer spotted the Tim Holt 'Death Wheel' comic book, he liked the fact it represented some or all of his killing methods, and simply chose it because of its menacing touch. However, he may have chosen it because of the pseudonym he had grown so attached to- a pseudonym he would seemingly place at the foot of the 340 cipher.
The 'Wheel of Fortune' or 'Rota Fortunae' has a long and rich history, crossing many cultures and eras. Here is an excerpt from Wikipedia:
"In medieval and ancient philosophy the Wheel of Fortune, or Rota Fortunae, is a symbol of the capricious nature of Fate. The wheel belongs to the goddess Fortuna (Greek equivalent Tyche) who spins it at random, changing the positions of those on the wheel: some suffer great misfortune, others gain windfalls. Fortune appears on all paintings as a woman, sometimes blindfolded, "puppeteering" a wheel."
The great windfall may be the promise of paradise, but the downside is the servile nature expected by the one who summoned you.
But here is the interesting part- again taken from Wikipedia. 
"The origin of the word is from the "wheel of fortune" - the zodiac, referring to the Celestial spheres of which the 8th holds the stars, and the 9th is where the signs of the zodiac are placed. The concept was first invented in Babylon and later developed by the ancient Greeks. The concept somewhat resembles the Bhavacakra, or Wheel of Becoming, depicted throughout Ancient Indian art and literature, except that the earliest conceptions in the Roman and Greek world involve not a two-dimensional wheel but a three-dimensional sphere, a metaphor for the world. It was widely used in the Ptolemaic perception of the universe as the zodiac being a wheel with its "signs" constantly turning throughout the year and having effect on the world's fate (or fortune)." link.
The zodiac is an area of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The paths of the Moon and visible planets are also within the belt of the zodiac. The Zodiac is divided into 12 signs beginning with Aries and Taurus.
The Zodiac wheels have multiple cultural adaptations, shown here in a Wordpress blog:
"These zodiac/time wheels are not common in Eastern Orthodox iconography, but they are found in one variation or another occasionally — usually, as here — in the form of wall paintings in churches. When seeing such a “Wheel of Time” — also called a Wheel of Life — one cannot help thinking of those Tibetan images that also represent a wheel of life as the “Wheel of Becoming” — in this case a wheel of rebirth:"
Here is one final extract from the book 'Deep Value:
Plutarch says that Servius knew "fortune is of great moment, or rather, she is everything in human affairs" because it was through good fortune that he had ascended from slave to king. In Roman mythology Fortuna was the goddess of fate, and the personification of chance. She turned the Rota Fortunae- the Wheel of Fortune- which dictated the destiny of man." Therefore, did Zodiac dictate the destiny of his victims-  By Fire, By Gun, By Rope and By Knife- the very reason the 'Wheel of Death' portrayed on the Tim Holt comic was so very appealing.

The discovery by Tahoe27 linking the Tim Holt comic was fascinating in so many ways, yet, it may not have been the inspiration behind the 'Halloween' card, but the inspiration behind the 340 cipher and its accompaniment- the '13 Symbol' cipher.
If the Zodiac Killer had done his research and discovered the 'Wheel of Fortune' or 'Rota Fortunae', and its connection to the word 'Zodiac', then the Tim Holt comic may have been a gift from heaven- an offering he just couldn't resist. 
Five weeks after the November 8th 1969 340 cipher, the December 16th 1969 'Fairfield' letter may have shown the early machinations of the Zodiac design, appearing in rudimentary code- the full explanation of which would have to wait until October 27th 1970..
The interconnectivity between the 'Halloween' card, Tim Holt 'Death Wheel' comic, the pseudonym 'Zodiac' and the 340 cipher is an intriguing and perplexing blend of mystery. One that came together by deliberate intent, or came together from the mind of somebody wishing it were true.

This is a continuation of the article 'The Illusion of the 340 Cipher,' attempting to show Zodiac's second code was nothing more than a collection of puzzles, interconnected to his other mailed correspondences.   
The 'Halloween' card mailed by Zodiac on October 27th 1970 predominantly featured within the 340 cipher, in that, Paradice and Slaves was able to be shown bisecting the cipher horizontally and vertically across its mid-section, along with 'by' being found in all four quadrants. The text of the stamp 'In the Beginning God' fitted nicely on the first line of the cipher, with the word 'God' aligning nicely with characters 15, 16 and 17. In addition, the half-earth image on the stamp mirrored exactly with character 16.
The idea that all these connections to the 'Halloween' card, '13 Symbol' cipher and 'Exorcist' letter could be forged within the 340 cipher by chance, was presented as so unlikely, they must have been created by design.
The darkened section of the 'Halloween' card inner reads like an instruction manual. The skeleton's finger of 4-TEEN directing us downwards 14 lines, to find the word 'BOO.'
The 14th line containing four shaded circles, three of which can be formed into the word BOO, complete with exclamation mark (I + black circle).
The next feature on the 'Halloween' card is the strange symbol.  
​  

The following two characters on the 14th line of the 340 cipher can easily be rearranged, by reversing the letter F and attaching its adjacent character, to mimic the strange symbol on the 'Halloween' card. 
​The next feature on both the 14th line and 'Halloween' card is the letter N and the letter Z. Rotating the N ninety degrees clockwise forms the completed sequence of BOO!, strange symbol and letter Z on the 340 cipher.
This is achieved using 8 characters on the 340 cipher, all in close proximity to each other. Just like 'In the Beginning God' and 'Paradice and Slaves,' is this another stroke of luck, or has this been deliberately fashioned by the Zodiac Killer as part of a game. 
It is further apparent that the word 'BOO' (in reverse) bisects the word 'Paradice' running vertically down the cipher, separating the letters I and C.
On the 'Halloween' card in this approximate area, the Zodiac Killer has mirrored the letter N, which may or may not hold some significance.
This could be a case of simply looking for patterns and finding them, but with so many having now been unearthed, is this compounding evidence to reliably dismiss the 340 cipher as harboring a coherent and uniform message, as demonstrated by the 408?
The Zodiac Killer may have dropped several clues in his later communications, resisting the temptation of giving us the final solution:
"But, then why spoil the game."    

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.

On the left is the Fairfield letter mailed on December 16th 1969. 
Nine days prior to this communication another Fairfield letter was received, dated December 7th 1969 (see below). It is highly likely, based on the handwriting and tone of each correspondence, that they were penned by the same hand. Many have questioned these two letters as being genuine Zodiac material, however, there is every reason to consider them as being true Zodiac correspondence based on several factors.
Without knowledge of these 'dubious' letters existence or having seen them in any newspapers, it would be uncanny how the Zodiac Killer would continue the theme of these two letters into the 'Melvin Belli' letter on December 20th 1969, the 'My Name is..' letter on April 20th 1970 and the 'Button' letter mailed on June 26th 1970. In other words, three of his next four communications. Here is the theme running consecutively, starting with the December 7th 1969 letter: 
"I just need help. I will kill again so expect it any time now. The will be a cop. Then I will turn myself in OK. I will kill in SF 3 times (including cops). The one thing I ask of you is this, please help me. Please help me I cannot remain in control for much longer. But there is more glory in killing a cop than a cid because a cop can shoot back. I shot a man sitting in a parked car with a .38".
It is clear from the December 7th and 16th communications the author is threatening 'government life'- most likely the police. In the December 7th 1969 communication the author has supplied a code containing 38 characters, followed by the December 16th 1969 letter threatening another 38 kills including cops, and curiously in his June 26th 1970 'Button' letter, the claim of shooting "a man with a .38." Most likely coincidence, but you never know. 
Here is a forum thread on Zodiac Killer Site with some of the same salient observations, particularly by AK Wilks.
The 38 character December 7th 1969 Fairfield letter (below) has been cleaned up and darkened to make the letter more readable. Not all the code is very clear, so has been interpreted from what we know of the Zodiac Killer's other codes and ciphers (The final line could hold a 'boxy style' C, but has been interpreted as a square. The B on the second line is also questionable).   
"I just need help. I will kill again so expect it any time now. The will be a cop. Then I will Turn myself in    OK."

Was this code a crude attempt at pushing us in the right direction regarding his infamous 340 character cipher mailed just one month earlier. The obvious similarities are there, particularly the first four characters of this code mimicking the opening four characters of the 340 cipher, and the last five characters of each code in both instances. It certainly isn't difficult to spot an inference to 'Zodiac' once again, possibly indicating its importance within the 340 cipher. 
A hoaxer could easily have copied elements of the 340 cipher and incorporated them into, what many believe, a poor imitation of a Zodiac correspondence. But if the Zodiac Killer hadn't seen either of the two Fairfield letters, do we attribute the continuing theme through three of the next four genuine Zodiac correspondences as just sheer luck, referring to "needing help" and his suggestion of "killing a cop."  Additionally, from the 'double event' November 8th/9th 1969 contact, we have effectively been given four ciphers or codes (whether crude or not) in five correspondences. 
These observations may lend more credence to the Fairfield communications, and their rightful place as having been penned by the hand of the Zodiac Killer. 
​THE MESSAGE WITHIN THE FAIRFIELD LETTER

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. ​

We certainly cannot take the early victim count of the Zodiac Killer as gospel, but bearing in mind the confidence of many regarding the murders of Robert Domingos (18) and Linda Edwards (17) on June 4th 1963 as possibly the precursor to the Lake Berryessa attack, the murders of John Franklin Hood (24) and Sandra Garcia (20) on February 21st 1970 appear a little under-reported. The Melvin Belli letter mailed on December 20th 1969 indicated the Zodiac Killer may have been looking for a ninth and possibly tenth victim- so bearing in mind his propensity of searching for a couple, this double murder is certainly in the correct timeframe, exactly bisecting the Melvin Belli and '13 Symbol' cipher letter on April 20th 1970. In addition, this letter would claim ten victims.
The young couple had traveled to East Beach, Santa Barbara, near East Cabrillo Boulevard on Saturday afternoon, with John telling his parents he was to spend the day with his fiancee. Sandra had informed her parents that they "wouldn't be gone long." When they didn't return home that night the families were understandably concerned.
Their bodies were discovered early Sunday morning by beachgoers, fully clothed underneath a blanket. They had been brutally beaten and stabbed, predominantly in the back and face. John Hood had been stabbed eleven times, but it appears Sandra Garcia suffered far worse, not dissimilar to the attack on Bryan Hartnell and Cecelia Shepard at Lake Berryessa on September 27th 1969. Had the Zodiac Killer returned to a familiar method of execution after his venture into the heart of San Francisco, and was the Melvin Belli letter the foreboding of a man who had lost control once again. 
The Oxnard Press Courier of John Franklin's home town reported the murders on February 23rd 1970: "Oxnard Man, Fiancee Murdered Victims. Bodies Found on Beach; Man was decorated veteran John F. Hood found slain with fiancee. The brutally stabbed and beaten bodies of a highly decorated Vietnam veteran from Oxnard and his attractive fiancee were discovered Sunday on an east side Santa Barbara beach just below a cemetery. Police identified the victims as John Franklin Hood, 24. who was discharged from the Army last month with the rank of staff sergeant after a combat-filled year in Vietnam, and Sandra Garcia, 20. of Santa Barbara. Early-morning beachgoers discovered the fully-clothed bodies under a blanket and hailed a passing patrolman. Police immediately closed off the area and later gave some brief details. However, they did not release some information for what they termed was a “good reason.” Detectives have questioned relatives and friends of the victims in an effort to trace the steps that led them to that beach." 

Continued - Page 2 of above article: "by Oxnard police. After the bodies were moved police found a 9 inch bone-handled fish knife in the sand. Santa Barbara authorities said the knife, possibly the murder weapon, had a 4 inch blade. Hood was stabbed 11 times in the face and back. The girl had multiple stab wounds, and authorities said she was not sexually molested.
Both bodies were discovered face-down, apparently left that way to give the appearance that the victims were sleeping, authorities said. 
The Hood family drove to Santa Barbara last night to be with Sandra's parents, Mr and Mrs Cruz Garcia, 3088 Calle Pinon, who were reported under heavy sedation. The families said "they had no idea" as to what happened at the beach. There were no difficulties and neither of the victims had any enemies as far as the families knew. Police said their investigation would continue. 
The eldest of six children, Hood was born in Seattle. He came to California with his family in 1950. He attended El Rio Elementary School and graduated from Camarillo High School in June, 1965. After graduation, he worked at Wimpy's Drive-In in Oxnard and then joined the Army in January 1966. He spent two years in Germany with the 64th Armored Division after boot training in Ft. Bliss, Texas, and then returned home for leave before being sent to Vietnam. While on leave, Hood met Sandra while they were both vacationing in Tijuana, Mexico. An expert marksman, Hood was sent to Vietnam on January 6, 1969 with the 64th Armored Division. Hood was closed-mouthed about the combat-filled year he spent there and about the Silver Star, Bronze Star, Purple Heart and other medals he had received for valor. After returning to Oxnard, he went back to work for the drive-in eatery. Although Hood and Sandra were planning to be married, they had not set a wedding date.
Besides his parents, Hood is survived by his sisters, Mrs Linda Jean Ortiz, 19, Lauretta Ann Hood, 16, and Virginia Sue, 13; and two brothers Jerry Allen, 18, and Joseph William, 10. The elder Hood is employed with the Associated Concrete Co, Saticoy, and Mrs Hood drives a small school bus. Hood's fiancee had been an employee of the State Motor Vehicle Department in Santa Barbara. Her father is the owner of the Garcia Auto Wrecking Co, Besides her parents, she is survived by three brothers."  Oxnard Press Courier, February 23, 1970.  

​February 24th 1970: "Police Hunt Pair In Twin Murders Santa Barbara. Detectives today were combing their city for two young men wanted for questioning in the vicious knife-slaying of an Oxnard Vietnam war veteran and his pretty Santa Barbara fiancee. Detectives said the pair, both in their early 20s, were seen “washing cut wounds” at an east beach area service station near where the bodies of the couple, John Franklin Hood, 23, of 460 Helsam Ave, and Sandra Garcia, 20, of 3088 Calle Pinon, Santa Barbara, were found. Witnesses told detectives the two men walked into the station about I a.m. with cut wounds they said they had received as the result of a fight in the east beach area. Detectives said one of the men had a vertical cut across the center of his forehead, extending from his hairline to an eyebrow. The other man had a wound on the back of his right hand. They were seen driving an early 1950 vintage light blue sedan with primer spots on the right side and trunk deck. Pathological tests revealed Hood and Miss Garcia were killed sometime between IO p.m. Saturday and 2 a.m. Sunday. The tests were conducted by Dr. John P. Blanchard, pathologist there." 
Oxnard Press Courier, February 24, 1970. 

Early details of crimes are usually withheld, though it later became apparent the killer had murdered the young couple with a 4 inch bone-handled knife, partially buried in the sand underneath the blanket. Why the killer failed to take the knife with him can only be speculated upon.
Whether this was the Zodiac Killer venturing south to commit this double murder may never be known, but bearing in mind the murders were in the correct Zodiac timeline, the only reasonable approach with such limited information available, is to examine his following correspondence- the April 20th '13 Symbol' cipher.
This correspondence and cipher has been analyzed with a view to the code giving us a name.
However, the introduction: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is ------," leaves us with the possibility we are not looking for a name within the code, we were in fact, simply supposed to fill in the blank. Later in the communication he states "I have killed ten people to date" and "I hope you have fun trying to figgure out who I killed."​​​ Was this a subtle clue, that we are supposed to be figuring out a date to unlock who his ninth and tenth victims were. By the sheer law of averages of his known victims, he attacked a couple 75% of the time. He also never claimed a ninth victim independently  between December 20th 1969 and April 20th 1970. 
The Zodiac Killer used symbols in his ciphers, so we will strip the '13 Symbol' cipher back to basics to attempt to uncover his intentions. He gave us three Taurus symbols and an Aries symbol reversed. He also gave us three circles.
The '13 Symbol'  cipher was mailed on April 20th, which is the exact date the star sign switches from Aries to Taurus.
The blank or white circle is the symbol for a full moon. See 1970 calendar. The astrological signs and full moon symbol are both relevant to the calendar.
The Zodiac Killer has placed the Taurus symbols within the circles- so by simple wordplay we have 'full moon in Taurus'.
The only 1970 full moon in Taurus is April 21st. If we are 'trying to figure out who he killed,'  the figure 21 isn't a bad place to start. The next thing to tackle, is the reasoning behind the Zodiac Killer giving us three full moon symbols. Because he is challenging us to discover who he killed, it isn't unreasonable to assume the three full moons play a significant part in this game. The '13 Symbol' cipher gave us the first full moon, so we will look back at the last two Zodiac events.

One month prior, Kathleen Johns, accompanied by her 10 month old daughter Jennifer, were traveling along Highway 132, west of Modesto, en route to Petaluma, California, when her routine journey turned upside down. She was to make the near fatal mistake of stopping on a deserted highway at approximately 11.45 pm at night, ushered to the side of the road by a passing motorist, flashing his headlights and gesturing towards her 1957 Chevrolet. Believing he was indicating a fault with her vehicle, Kathleen Johns drew over to the side of the road. The man explained that her wheel appeared loose, offering to tighten it up for her, and she duly obliged. This innocent error was to begin a chain of events that are still not fully understood to this day, and have initiated countless years of debate on whether the man who approached Kathleen Johns car that fateful night was actually the Zodiac Killer, and the 'proposed madman' responsible for unleashing terror in the Bay Area of Northern California, and bringing the 'Summer of Love' into the summer of fear just two short years later.
Kathleen Johns was 'abducted' just before midnight on March 22nd 1970 and escaped at approximately 1.50-2.00 am on March 23rd 1970. March 22nd was as full moon. This is our second full moon. The third, with the figure 21 in mind, must be the date that Zodiac was asking us to "figure out". Therefore, we will travel back to the previous full moon.
John Franklin Hood and Sandra Garcia, were not only are a couple, but a couple who were murdered under the Berryessa template, which fell on the full moon day of February 21st 1970, to give us our third full moon as depicted in the '13 Symbol' cipher. 
https://www.timeanddate.com/calendar/1970