On October 27th 1970 the Zodiac Killer mailed the Halloween card to the San Francisco Chronicle, stating "sorry no cipher" in the form of a cross, and fashioning "Paradice" and "Slaves" in the same manner. In the four corners he placed By Fire, By Gun, By Rope and By Knife. For anyone who believes the September 27th 1969 Lake Berryessa attack was at the hand of the Zodiac Killer, must surely conclude the "by knife" reference on the Halloween card to be admitting his participation in this crime, as this phrase on the car door had been withheld from the public and newspapers alike. This inextricably links the author of the Halloween card to the Lake Berryessa attack. Elements of the Halloween card can be found in the 340 cipher, with "Paradise" and "Slaves" bisecting the cipher (17 X 17) horizontally and vertically, with the word "by" placed horizontally in each of the four quadrants. 

The Halloween card alliance to the Lake Berryessa attack formed "by knife", in conjunction with the knothole in the tree and the wording "peek-a-boo you are doomed", should leave little doubt the two are connected. There is also a strong connection from the Halloween card to both the December 7th 1969 and December 16th 1969 Fairfield letters, and in turn, all three to the 340 cipher. The December 16th 1969 Fairfield letter contained a crude arrangement of 9 symbols (10 including the large crosshairs), impossible to decode as it stood. The four crosshairs around a larger version looked extremely similar to the Halloween card arrangement - and bearing in mind the December 16th 1969 Fairfield letter was accompanied by a crude drawing of a knife entitled "The Bleeding Knife of Zodiac", it seemed likely the short code may have been Zodiac's initial attempt at revealing the hidden words on the car door of Bryan Hartnell's 1956 white Karmann Ghia. 

Thanks to Tahoe 27's excellent find linking the Halloween card to a Tim Holt comic book, depicting Death By Fire, Death By Gun, Death By Rope and Death By Knife, it seemed obligatory to consider the connection from the Halloween card "by knife" to the "The Bleeding Knife of Zodiac", along with the similarity in design between the Paradice/Slaves arrangement and the four crosshairs circling a larger version. The four methods of death represented by the four crosshairs or targets.   

The Halloween card, 340 cipher and both Fairfield letters seemed intertwined. The fact that Zodiac placed "sorry no cipher" in the form of a cross rather than just singularly, can be linked to "Paradice" and "Slaves", and therefore the 340 cipher. Was he suggesting the 340 cryptogram was not a true cipher? It appeared he may have been dropping clues to the design of the 340 cipher as early as December 7th 1969, placing a 38 character code in the first Fairfield letter.

On the left, "by" can be observed in all four quadrants. Parts of the December 7th 1969 code are highlighted in blue, while four of the adjacent symbols from the December 16th 1969 code are highlighted in yellow.

The December 7th letter opened with the words "I just need help", reminiscent of the December 20th 1969 Melvin Belli letter, and followed by "I will kill again, so expect it any time the will be a cop", similar in fashion to the April 20th 1970 letter, where Zodiac stated "But there is more glory in killing a cop than a cid because a cop can shoot back". The December 16th letter opened with the same two words as the December 7th letter, stating "I just want to tell you", almost certainly tying them together - along with the handwriting and crude coding. Bearing in mind neither of the Fairfield letters appeared in the newspapers, it appears that Zodiac either just accidentally mirrored these communications with the subsequent December 20th 1969 and April 20th 1970 letters, or he was the author of all four.

Was the Paradice, Slaves, By Fire, By Gun, By Rope and By Knife configuration a representation of the number of murders he was intending to secure for the afterlife. Paradice, Slaves, By Fire, By Gun, By Rope and By Knife oddly contained 38 letters. The character count on the December 7th 1969 Fairfield letter code was 38. The intended victims on the December 16th 1969 Fairfield letter was 38. The 340 'Dripping Pen' card, eerily similar to the "Bleeding Knife of Zodiac" depiction, opened with the wording "Sorry I haven't written, but I just washed my pen." This phrase again contained the words "I just", but also an alphanumeric count of 38. The April 20th 1970 letter, stating "I hope you have fun trying to figgure out who I killed" had a code that added up to 38 when the alphabet was placed alongside it.
And finally, the Exorcist letter (widely believed to be the final offering by the Zodiac Killer) claimed 37 victims, but promising to kill again if his demands were not met. Probably coincidence, but curious nonetheless.  

The 'Dripping Pen' card may have been a depiction chosen by the Zodiac Killer regarding his exploits at Lake Berryessa. The pen dripping blood as he is writing on the car door of Bryan Hartnell's vehicle, and his reason for washing it. The 340 cipher accompanying this card, with the "Paradice", "Slaves" and "by knife" link back to the Halloween card, further indicating a connection to Lake Berryessa through these communications. 

​The 'Death By Fire, Death By Gun, Death By Rope and Death By Knife' agenda could have been formed in the mind of the killer as early as the beginning of his campaign of terror, when he mailed the 408 cipher, stating  "the best part of it is that when I die I will be reborn in paradise 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 same paradice and slaves permeating through much of his correspondence, and possibly the 340 cipher also. "By knife" an integral part of both Fairfield letters and the Halloween card, to hopefully lay any doubts to rest, of his involvement and knowledge of the writing at the foot of the message on Bryan Hartnell's car door.

The December 16th 1969 "knife," in a side-by-side comparison to the writing on the car door of Bryan Hartnell. Anyone could have read about the Lake Berryessa attack on Bryan Hartnell and Cecelia Shepard with a knife, but would an impostor have emphasized it in the form of a drawing, as to signify its importance, without knowing for certain the hidden message on the car door? And how would the Zodiac Killer, when designing the Halloween card, accidentally mirror the "death by fire, gun, rope and knife" arrangement on the Fairfield letter, when the December 16th 1969 letter was never published in the newspapers. Somebody attempting to imitate the Zodiac Killer in both December letters, would surely have attempted to imitate him, not go out of their way to undo the neatness and organization exhibited by the 340 cipher and thereby nullify their efforts? The Zodiac Killer would have had no such concerns.

The Zodiac mailed correspondence to the San Francisco Chronicle on April 20th 1970, in which he stated "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." Suisun City, Solano County, California can be seen via the link to border the city of Fairfield. But why is this relevant?
It has been suggested in previous articles that the Zodiac Killer may have resided near the payphone at Springs Road and Tuolumne Street, but we know that two letters were mailed from Fairfield to the San Francisco Chronicle on December 7th 1969, and to the San Francisco Examiner on December 16th 1969. If these were genuine Zodiac letters, then there is a possibility that he may have been a resident of Suisun City or Fairfield for the duration of the 7th to 16th of December and mailed his letters from this location. Was he a resident of this area beyond December 16th 1969, or did he reside here permanently? The Bay Area murderer may have had two residences, a vacation home, lockup or a business in this region of Solano County. 
Just a matter of weeks after the final Fairfield letter, floods in Suisun City/Fairfield, "from Laurel Creek and Union Avenue Creek caused flooding in January 1970" resulting in the evacuation of many "residences and businesses" in the area. The Zodiac Killer then wrote to the San Francisco Chronicle in April, stating "that my bus bomb was a dud.  I was swamped out by the rain we had a while back." But was he telling the truth?  

# The population of Suisun City was only 2,917 in 1970.
# The population of Fairfield was 44,146 in 1970.

We know the Zodiac Killer mailed his first three letters simultaneously on July 31st 1969, but what inspired him to design a trinity of cryptograms that when combined formed an almost complete and uniform message. It is likely he split the cipher into three parts for maximum newspaper coverage, however, we know little of what inspired him to design the codes in the first place.
The 'Zodiac Killer' pseudonym may never have existed had it not been for the skepticism of Vallejo Police Chief Jack E Stiltz, who insisted the three time murderer send more details to prove he was the 'cipher killer'. It was reasoned that something Zodiac read in the Sunday August 3rd 1969 San Francisco Examiner & Chronicle inspired him to repackage himself from "the murderer" to "the Zodiac". So, what drove the killer of David Faraday, Betty Lou Jensen and Darlene Ferrin to include a cryptogram alongside his deadly deeds and threats. The short answer is, nobody knows for sure- but we do know it took the Lake Herman Road double murderer just over seven months to finally begin his letter writing campaign. Was the killer always planning to kill again and write to the newspapers, or was it the extensive press coverage that inspired him to rise to the picture being painted of him. 
It seemed Detective Sergeant Leslie Lunblad beat a lone furrow in the pursuit of the murderer, but he was ably assisted throughout by many agencies, including the Criminal Investigation Bureau in Sacramento, Vallejo Police Department, Napa and Sanoma County sheriff's departments and Sergeant Jack Richard Oller, an investigator in the Fairfield office of the sheriff's department.  Jack Oller moved to Oakland, California in 1929 and served in the U.S. Army as a combat engineer in Europe. In 1978, he retired from the Solano County Sheriff Department with the rank of lieutenant.
Along with the Zodiac murder of Paul Stine on October 11th 1969 and the November 21st 1969 San Jose letter and cryptogram, we effectively had the entire shopping list of threats tabled in the 'Fairfield' letter, mailed on December 16th 1969. His threat of 'this state is in trouble..I will go for the Goverment life' may be traced back to a Sunday Times-Herald article on March 30th 1969, in which these law enforcement agencies were pivotal in the search for the Lake Herman Road murderer, including Sergeant Jack Oller. The Zodiac Killer's threat on police in the 'Fairfield' letter centered around Fairfield, Sacramento and Oakland. 
The inspiration behind the July 31st 1969 letters and cryptogram is difficult to ascertain, but often with the Zodiac Killer throughout it was something he read that triggered a response, such as the 'Debut of Zodiac' and 'Bus Bomb' letters.
The Sunday Times-Herald article on March 30th 1969 may or may not hold the answers, however, it was published four months prior to the July 31st trinity and did contain some noteworthy passages. Whether these were the trigger for the murderer to begin his letter writing campaign is pure speculation, but in the absence of alternatives it was worth considering.  
Here is the newspaper article in full:     

The youth, a scalor at Vallejo High, planned to make teaching his career. He was extremely active in Scouting, and was a member of the Interact Club at the high school.
"Last summer, he discovered girls" Mrs Faraday reminisced "but he hadn't done much dating- for one thing he could use the car only when I didn't need it to go to work." She is employed in the passenger reservations department at Travis Air Force Base. She said that when he did take the car for a date "he was good about observing curfews" (12.30 on Friday nights). "So I didn't think a thing about it that night. I was asleep when the phone rang at 3 am."
Mrs Faraday conversed with total composure, although the wounds haven't healed and won't. The same was true of the Jensens. Nothing in his 21 years as an army officer had prepared Lt Col. Verne Jensen for the shock of his younger daughter's death, however. He retired in 1963, decided to remain in Vallejo and now is employed as supply officer for the General Services Administration in San Francisco. The Jensens, with their elder daughter, Melodie, live at 123 Ridgewood Ct. " I don't feel vindictive" he mused "but I am apprehensive. I feel some nut is on the loose."
His words could have been uttered by Mrs Faraday, who said her principal concern that the killer be found was not based on vengeance but on her fears there may be further victims. "And, he'll find it easier the next time."
She said the other three Faraday children Debra, Robert and Steven "have handled the situation very well, I think. Presumably they have long and happy lives ahead of them, and they've got to live them."
The Jensens' lives remain clouded by the tragedy. "We'd like to have her back" Mrs Jensen said wistfully. "It took a lot to bring her this far."
At Hogan High Betty was an excellent student, a junior, she was hopeful of winning an art scholarship and she worked extremely well in several forms, some of which were displayed as I talked to the family. All three shook their heads negatively when asked if they had any ideas to the perpetrator. "We know he's a nut, but what kind of nut" Mrs Jensen replied. She added she was dubious about anything worthwhile could be gained in once again turning the spotlight on the murder case. "But we'll do anything we can to help" she declared.
As for the investigation's progress, Lublad said there has been considerably more than might be gleaned from news accounts of it. "If I talk to a suspect, I'll know positively whether he was there that night" he said cryptically. Beyond that, he would not comment. ​​

It is not difficult to cherry-pick certain phrases and words to fit ones agenda, however, we must consider that the murderer of David Faraday and Betty Lou Jensen likely read this article, and was buoyed by the description of his exploits as a "horrifying crime that may very well be the most celebrated murder mystery currently under investigation in California."
David Faraday's mother summed up her fears: "who said her principal concern was that the killer be found, not based on vengeance but on her fears there may be further victims. "And, he'll find it easier the next time."  
She wouldn't have to wait long for the killer to live up to her fears, promising he would "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."  
Detective Sergeant Les Lunblad's support may too have not gone unrecognized, with his assistance from a "score of law enforcement agencies in the state," including Sergeant Jack Richard Oller and the Fairfield Office.
If this newspaper article was the last major feature regarding the Lake Herman Road slayings, before the killer began his July 4th 1969 attack on Michael Mageau and Darlene Ferrin at Blue Rock Springs, then it is rather unusual that the ​Sunday Times-Herald article on March 30th 1969 would finish with the thoughts of Detective Sergeant Les Lunblad:in such a manner:
"If I talk to a suspect, I'll know positively whether he was there that night" he said cryptically.
Four months later, the murderer stated "I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife," and he too said it cryptically.    

Here we will take a further look at the two letters mailed from Fairfield to the San Francisco Chronicle on December 7th 1969 and the San Francisco Examiner on December 16th 1969. Many have dismissed these two communications as having been penned by the Zodiac Killer, but either way, they were almost certainly written by the same individual. The most important question to ask - is were these letters ever publicized in the newspapers during the December of 1969. They seemingly got no coverage in the San Francisco Chronicle or Examiner newspapers, but did they appear in any other publication? If not, then there can be little doubt these two Fairfield letters were mailed by the Zodiac Killer. 

The article on the left appeared in the San Francisco Chronicle on December 28th 1969, regarding the letter mailed to attorney Melvin Belli on December 20th 1969. It states "The Zodiac Killer-unheard of in recent weeks-is back in operation and pleading for help before he takes his ninth and tenth victims."
The Melvin Belli letter was mailed only 13 days after the December 7th 1969 San Francisco Chronicle 'Fairfield' letter, so it appeared as though the Chronicle had dismissed the Fairfield letter claiming they had not heard from Zodiac "in recent weeks." They apparently never published the Fairfield letter (unless anybody knows otherwise), and the follow up letter on December 16th 1969, mailed to the San Francisco Examiner equally appeared to make little impact. Why were these communications apparently overlooked? 
Many Zodiac researchers and enthusiasts regard the two Fairfield letters to have been penned by a hoaxer- but if the letters were created by a hoaxer why did he do such a poor job as to negate the purpose of sending them.
The Zodiac Killer created two organized and structured ciphers of 408 and 340 characters. Both were designed with care, using seventeen characters in each row, and a form of 'filler' on the 408 code to keep the cipher symmetrical. The December 7th 1969 Fairfield letter contained a 38 character code, much of which was 'stolen' from the 340 cipher and formed into scruffy disorganized rows. If the letter writer was attempting to disguise himself as Zodiac, then why didn't he simply create a few lines of symbols in an organized fashion like the 408 and 340 cipher.
The fact he didn't do this could suggest that he wasn't trying to pass himself off as Zodiac- because he was Zodiac. 
The argument, is that the December 7th 1969 letter is a poor Zodiac imitation and therefore not the Zodiac. However, it isn't very difficult to copy any of the characters from the first two ciphers and create a new and realistic looking cipher that mimics its predecessors. This is not a difficult task- and neither is the handwriting.
The following image (December 7th 1969 Fairfield letter and 38 character code) was inspired by a forum thread on Zodiac Killer Site.

The December 7th 1969 letter stated "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." 
If this letter was by a hoaxer and not published in any newspapers, then how was the Zodiac Killer able to know its contents.
The December 20th 1969 'Melvin Belli' letter was confirmed Zodiac correspondence, as it contained a piece of Paul Stine's bloodied shirt. The Melvin Belli letter pleaded for assistance "Dear Melvin. This is the Zodiac speaking. I wish you a happy Christmass. The one thing I ask of you is this, please help me. I cannot reach out for help because of this thing in me won't let me. I am finding it extreamly dificult to hold it in check I am afraid I will loose control again and take my nineth & posibly tenth victom. Please help me I am drownding. At the moment the children are safe from the bomb because it is so massive to dig in & the triger mech requires much work to get it adjusted just right. But if I hold back too long from no nine I will loose complet all controol of my self & set the bomb up. Please help me. I can not remain in control for much longer." Can it be argued that the Fairfield letter stating "I just need help" and the Melvin Belli letter thrice urging "please help me" just 13 days later, was just simple coincidence, or is it more likely the Zodiac Killer had written the earlier Fairfield letter and was just continuing the theme. In addition, the second part of the December 7th Fairfield letter is threatening to kill a cop just like the communication following the Belli letter on April 20th 1970, in which Zodiac suggested "there is more glory in killing a cop than a cid because a cop can shoot back." 
Additionally. the Fairfield letter after stating he "needs help," intimates he "will kill again," as does the Melvin Belli letter when warning he "will lose control again." 

Now let us approach this from a different angle and consider the possibility that the December 7th 1969 letter was featured in the Fairfield Daily Republic newspaper, or some other publication prior to the Zodiac Killer composing the Melvin Belli letter.
The Zodiac Killer certainly appeared to design his ciphers in a carefully structured way- so imagine- that when saw this poorly designed and crude 38 character code plagiarizing his 340 cipher in a newspaper- why on earth would he then validate the hoaxer by mimicking the December 7th 1969 letter by stating "please help me" in the Melvin Belli letter later that month. One would think he'd have wanted to disassociate himself from it. 
Whichever approach you pursue, tends to validate the December 7th 1969 letter mailed to the San Francisco Chronicle, and by association, the December 16th 1969 letter mailed to the San Francisco Examiner, which was almost certainly penned by the same author. The latter Fairfield letter could also have links to the 'Halloween' card, with the code reading Death By Fire, By Gun, By Rope and By Knife. link    

Much has been made of the single postage on both the Fairfield envelopes, the writing paper used by the author and the crudeness of the two short codes. However, there could be a perfectly reasonable explanation for all these anomalies.
The Zodiac Killer thought he had sent proof of his connection to the first two crimes when he mailed the trinity of July 31st 1969 letters. Vallejo Police Chief Jack Stiltz urged the author for more details to prove he was the killer, and the Zodiac duly obliged on August 4th 1969. The Zodiac then mailed a piece of taxicab driver Paul Stine's shirt in his next three consecutive and 'confirmed' communications. Firstly, in the October 13th letter, secondly, with the November 8/9 card and letter, and finally with the Melvin Belli letter.
All these communications were mailed from San Francisco, likely during his normal routine- but the December 7th & 16th letters were mailed from Fairfield. If he was away from his usual residence during this span of 10 days (possibly having broken up for Christmas) and was on holiday, or visiting family, or simply away from his home location on business, then it is conceivable that he had to improvise with writing paper and stamps. He most certainly would have stored the bloodied shirt piece in a secure location (possibly at home), to which he likely had no access during the mailing of the two Fairfield letters. These letters have all the hallmarks of 'spur of the moment' communications while away from his home location. 
This may explain their deviation from what had come before or after. It is, nevertheless, crucial to find out if these two Fairfield letters were published by any newspapers prior to December 20th 1969. If they weren't published, then the two Fairfield letters are almost certainly penned by the Zodiac Killer. 

In 2013 Tahoe27 made an excellent discovery, possibly linking the 'Halloween' card with a Tim Holt comic featuring the 'Wheel of Fortune' or 'Rota Fortunae.' The cover displayed the four methods of death used by Zodiac on his 'Halloween' card configuration, that of 'Death By Gun', 'Death By Knife', 'Death By Fire' and 'Death By Rope'. However, the discovery may be far greater than first considered, with the 1952 Tim Holt comic the source behind the design of the 340 cipher rather than the Halloween card. The 'Halloween' card was just the confirmation that the 340 was not a cipher at all, hence the crossed "sorry no cipher" addition on the inside of the envelope, linking the Paradice and Slaves configuration back to the November 8th 1969 offering.
​See 'Zodiac admitted 340 not a real cipher' [pt1].' 
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, claiming a potential 38 more victims.
The 'Fairfield' letter 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. There are two key features of this correspondence possibly linking it to the 'Halloween' card, and more importantly, to the Tim Holt comic. The second we will deal with later, but the first is the rather childish looking or amateurish offering of a code consisting of only nine characters.
Clearly, the Zodiac must have known that offering just five different symbols in a code of nine is open to many different interpretations and therefore 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 '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. 

The November 8th and 9th 1969 communications came as one package, and he certainly wasn't going to reveal the workings of the 340 cipher after just one day in the 'Bus Bomb' letter, so the December 16th 1969 (or possibly December 7th 1969) 'Fairfield' communication was effectively the Zodiac Killer's first communication after the 340 cipher. Can we again call it coincidence that, not only did the Fairfield offering give us a further code, but 'Death By Gun', 'Death By Knife', 'Death By Fire' and 'Death By Rope' would fall readily into its design, as would the 'Halloween' card configuration of Paradice and Slaves so readily mirror the 340 cipher- possibly bringing these three communications in line with one another. The second interesting feature of the Fairfield letter is the wording the author uses:
"This is the Zodiac speaking. I just want to tell you this state is in trouble. I will go for the Goverment life, so don't foreget me. I will kill more people than you cops can count, so look for more blood. You better print."     

The 'Halloween' card has become synonymous with either a threat of a fourteenth victim or the claim of a fourteenth victim, however, the number four may hold more significance within its design. The eyes are obviously of great importance to the Zodiac Killer- after all, he added twelve to the card inner, along with 4-TEEN and the unusual symbol.
He deliberately chose to separate fourteen, creating the number 4. He added four larger eyes outside of the tree, as well as placing four dots around the symbol. He also highlighted four eyes in red on the card outer and inner. 
The strange symbol (with the four dots) could be a joined Z, V and F, and being preceded by four eyes, could simply be interpreted as "look for Zodiac victim fourteen" or with respect to 4-TEEN, "look for number fourteen." 
Up to this point and beyond, none of Zodiac's confirmed or insinuated victims (Kathleen Johns, Cheri Jo Bates and Richard Radetich) lay undiscovered, so it is entirely plausible this card was referring to the disappearance of Donna Ann Lass 51 days earlier. The skeletons indicative of a body lain undiscovered for a measurable period of time.
The coloring of the four skeleton eyes may be suggestive of blood or death, a formula used in the creation of the '13 Hole' postcard on October 5th 1970, where the author added a pasted red crucifix to the card.
The 'Halloween' card could be telling us to "look for Zodiac victim fourteen" or equally "look for blood," as did the Fairfield letter on December 16th 1969, when the author stated "I will kill more people than you cops can count, so look for more blood. You better print."
This discovery by Tahoe27 on December 30th 2013 was certainly a great find, but it may just turn out to be the greatest find of them all. A discovery that may finally reveal the 340 offering to be masquerading as a fully fledged cipher, and as such, has had us chasing our tails for nearly half a century. Albeit, undecipherable at the time, the answer was probably staring us in the face just 38 days after the November 8th 1969 communication- in a letter many thought was penned by a hoaxer.

ZODIAC ADMITTED 340 NOT A REAL CIPHER [PT1]
ZODIAC ADMITTED 340 NOT A REAL CIPHER [PT2]

Courtesy of Zodiac Killer Site forum. These envelopes have been cleaned up using editing tools. 

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

'Rubislaw,' a regular contributor to this site, inspired me to take another look at the Fairfield letter, mailed on December 16th 1969.
​The correspondence stated "This is the Zodiac speaking. I just want to tell you this state is in trouble..I will go for the Goverment life, so don't foreget me. I will kill more people than you cops can count, so look for more blood. You better print."
The author then added the trademark crosshairs with a small code. The crosshairs had the same symbol in each of the four quadrants, with five symbols to its left. Decoding such a small sample could never be authenticated, however, an attempt will be made later in this article. 
The author attached a drawing of blood dripping from a knife, entitled "The Bleeding Knife of Zodiac."  Zodiac had previously claimed seven victims in the Bus Bomb letter mailed to the San Francisco Chronicle on November 9th 1969, so it wasn't surprising to see this knife drawing had 8 drops of blood falling from the blade. See here.
It is extremely difficult to pinpoint the inspiration for this letter, but here are a few notable events in December 1969.
The first being the murder of Meredith Hunter at the Altamont Free Concert on December 6th 1969 at the hands of Hells Angel Alan Passaro, who fatally stabbed and beat the 18 year old to death after he produced a revolver. This is not insinuating Alan Passaro was the Zodiac Killer, but bearing in mind the Hells Angels connection on Warren Avenue, Vallejo, and the drugs bust at The Cottage on Lake Herman Road in the run-up to the murders of David Faraday and Betty Lou Jensen, it was worth mentioning. Alan Passaro was later cleared of the murder, having deemed to have acted in self defense.
​ 
On the political front, bearing in mind the author was threatening to go for 'government life,' was the author referencing the troubles of the day. On December 1st 1969 the Selective Service System of the United States conducted two lotteries to determine the order of call to military service in the Vietnam War for men born from 1944 to 1950. These lotteries occurred during a period of conscription from just before World War II to 1973. It was the first time a lottery system had been used to select men for military service since 1942. The lottery numbers assigned in December 1969 were used during calendar year 1970 both to call for induction and to call for physical examination, a preliminary call covering more men. Taken from Wikipedia. For those believing in a Vietnam or military connection to Zodiac, was he responding with outrage to this lottery based conscription- threatening to attack 'government life'.
 
On December 12th 1969, the Desert Sun ran an article about 'Two Attorneys Jailed in Tate Murder Case.'
District Judge David Brown today sentenced two Los Angeles lawyers to 72 hours in jail and fined them $lOO each for trying to make a “press spectacular” out of the case of Charles D. Watson, charged in the Sharon Tate murders. "I am fining you $lOO and jailing you for 72 hours but I will suspend this provided you take the next plane back to California and shut your mouths,” Brown told the attorneys, Perry Walshin and David DeLoach. “I admonish you for making a circus out of my courtroom,” said the judge. Watson, dressed in green work clothes, made his first public appearance since he gave himself up Nov. 30 in I answer to a California murder I warrant. He since has been indicted on seven counts of murder and one count of conspiracy. Susan Denise Atkins, another, of a hippie band charged in the California murders, told a grand jury Watson was the one who killed Miss Tate with a knife. “Do you want to talk to these men or be represented by them" Judge Brown asked Watson today about the two California lawyers. “No, sir, I do not,” Watson said. “Do you want to see them” Brown asked. “No, I do not,” Watson replied. At least 30 Texas highway 1 patrolmen guarded Watson. At least 20 patrolmen and sheriffs deputies were in the courtroom. Watson, who grew up at nearby Copeville, Tex., was moved into the courtroom before 6:30 a. m. and no reporters or photographers were allowed near him. Leaving the courtroom, officers threw a coat over Watson’s head and hustled him past photographers. Walshin and DeLoach came to Texas last week. Walshin said he had represented Watson on the coast and that Watson’s mother wanted him in the case. link.

This article was published four days before the Fairfield letter and eight days before Zodiac's letter to attorney Melvin Belli.
Was the Fairfield letter actually written by somebody connected with the Manson Family, or an avid follower of the unfolding events. Tex Watson would ultimately be convicted of the seven counts of first degree murder he was charged with. The eight drops of blood on the 'bleeding knife' threatening a further murder, using Zodiac as the outlet.  
These are three unlikely examples of a possible inspiration for the Fairfield letter. Please post any further ideas in comments.

The final observation is regarding the code. The Zodiac Killer mailed the 'Halloween' card on October 27th 1970.
Was the Fairfield letter, if a Zodiac correspondence, the precursor to this card in rudimentary form. The Fairfield letter had four identical symbols in the four quadrants of the crosshairs. The 'Halloween' card contained four methods of death in the four quadrants, bisected by Paradice and Slaves, not dissimilar to the Fairfield letter.
Tahoe27 discovered a connection between a Tim Holt comic and the 'Halloween' card, regarding the wording  By Fire, By Gun, By Rope and By Knife. Is it possible the Fairfield letter symbols around the crosshairs represented these four methods of death? But what of the five symbols to the left. Take a look at the Tim Holt picture above.  

On the 'Dripping Pen Card' mailed on November 8th 1969 the Zodiac left us his running victim count, but this time he provided us several pointers by displaying the months. He wrote "Des, July, Aug, Sept, Oct = 7."  We know of Lake Herman Road (2) in December, Blue Rock Springs Park (1) in July, Lake Berryessa (1) in September and Presidio Heights (1) in October. That is five murders out of the seven he was claiming. That meant he was indicating either two murders in August, or just one in August and another in either of the other months. One consideration was the murder of Cheri Jo Bates on October 30th 1966, that he would belatedly claim in a future correspondence. However, his statement in the November 9th 'Bus Bomb' letter is telling: "This is the Zodiac speaking up to the end of Oct I have killed 7 people." This likely meant "This is the Zodiac speaking up to the end of Oct 31st 1969 I have killed 7 people. This doesn't necessarily rule out the Cheri Jo Bates murder, although without proof this is a Zodiac murder, or a murder under the umbrella of Zodiac, it is a curious statement.
Why did the Zodiac Killer specify the end of October, when his most recent murder by all accounts was the brutal slaying of Paul Stine on October 11th 1969. This could be interpreted as a sixth murder in August, and a seventh murder between October 11th 1969 and October 31st 1969. He would expand in his correspondence "I thought you would need a good laugh before you hear the bad news, you won't get the news for a while yet."  In view of his 'Bus Bomb' letter declaration that he would "change the way the collecting of slaves. I shall no longer announce to anyone. When I committ my murders, they shall look like routine robberies, killings of anger, + a few fake accidents, etc," this seventh murder may have been committed in the latter two thirds of October, detailed in the total, but not elaborated upon, and the suggestion that we wouldn't get the bad news for a while was somehow related to how or where the person was killed.     

There is, however, a completely different alternative, bringing into play the Melvin Belli letter on December 20th 1969. This correspondence stated Zodiac was in danger of looking for a ninth and tenth victim. The assumption therefore, was that victim number eight was probably killed sometime between the 'Dripping Pen' card on November 8th 1969 (or possibly November 9th), claiming seven victims and the Melvin Belli letter mailed on December 20th 1969. But again, taking the latter 'Bus Bomb' communication, Zodiac had claimed seven victims to end of October, not up to November 9th 1969. He did state seven victims on the 'Dripping Pen' card, but he added the extra hint that "you won't get the bad news for a while yet."
This may suggest that indeed, he had already killed again, prior to November 8th, but he simply wasn't announcing it to anybody, as the following communication would testify. We know that by the end of October (31st) the total was seven, therefore this unannounced eighth murder would had to have been committed from November 1st 1969 up to November 9th 1969. 
A contested piece of correspondence was the 'Fairfield' letter on December 16th 1969, claiming "I will go for government life." The accompanying drawing depicted the 'Bleeding Knife of Zodiac,' with eight drops of blood dripping from the weapon, suggestive of an eighth victim. Was this indicative of another Zodiac murder by knife, having been bolstered by his 'successful' attack in theatrical style, on Bryan Hartnell and Cecelia Shepard on September 27th 1969 at Lake Berryessa. Or, was the knife just a reminder to his last crime we know he committed. If this correspondence was genuine, the phrase 'government life' may indicate any person in any state run organization, with a distinct hatred towards officialdom unsurprising, bearing in mind his previous communications.
The question being, can anybody find the eighth murder spanning November 1st 1969 to November 9th 1969, in a relevant geographical location, that doesn't have the hallmarks of Zodiac. After all, he did state he would "change the way of collecting the slaves".  If this were the case, we simply wouldn't recognize it anyway.  

# A Salesian High School teacher, Daniel Williams had his house broken into, but nothing was taken. A man claiming to be the Zodiac Killer made several threatening phone calls beginning on October 23rd 1969, culminating with the caller saying "You're the dead duck" on November 2nd 1969. Later that day, Williams took a drink from the refrigerator, but fortunately spat it out after noticing a metallic taste. The drink contained enough arsenic to kill. Would a teacher be considered 'government life'. The date fits the criteria and the death could have appeared like natural causes, or a killing of anger.
Daniel Williams residence was situated at 1234 Bush Street, Martinez, only 9 miles from the location of Zodiac's first crime at Lake Herman Road.
http://www.zodiacciphers.com/zodiac-news/youre-the-dead-duck

An article in the San Francisco Chronicle by Paul Avery dated November 12th 1969 and titled "I've Killed Seven, The Zodiac Claims", clearly states 'As proof the letters were from the true Zodiac and not an imposter, the mass murderer enclosed another portion of the piece of shirt he tore off the body of San Francisco taxi driver Paul Stine'. Then in a second article on December 28th 1969 entitled "New Zodiac Letter...Fears He'll Kill Again", it states 'A few days after the Stine killing, Zodiac sent a letter to San Francisco newspapers and also included a swatch of Paul Stine's shirt. Another letter and another piece of Stine's shirt was sent to a Newspaper on November 11th'. See here. The 340 Cipher and Dripping Pen Card/Bus Bomb Letter were mailed in close succession on November 8th and 9th at the weekend and may have arrived at the beginning of the following week, accounting for the November 11th attribution. Then a Youtube documentary commencing at the 3 minute mark confirms that a total of three shirt pieces were sent. Two articles and one documentary, all indicating that a third section of Paul Stine's was sent accompanying either the 340 Cipher or Bus Bomb Letter.
Had the Zodiac Killer set aside three portions of shirt to send, it is highly unlikely he would want to be sitting on incriminating evidence for too long and after the murder of Paul Stine in Presidio Heights on October 11th 1969 he would mail his three portions of shirt with his next three correspondences. His first being the October 13th letter, just two days after the murder, his next letters were postmarked within one day of each other, so he sent the second portion with these and the final piece was mailed with the Melvin Belli Letter on December 20th 1969. What he didn't do however, was mail a piece of shirt with the Fairfield Letter on December 16th, four days before the Melvin Belli Letter, why, because it was a fake Zodiac letter, not mailed by the killer. This is not conclusive, but other features of the Fairfield Letter, suggest this correspondence was mailed by an impostor, who knew little about the mind of the real serial killer. 

It cannot be known for certain, but the Fairfield Letter seems to be suggesting a link to the Lake Berryessa stabbing on September 27th 1969, the only crime committed thus far with a knife. It was always questioned why the Zodiac failed to brag about his theatrical crime on the shoreline of Lake Berryessa, after all, it was his most daring to date. There is no definitive answer, but one thing the Zodiac Killer never foresaw, was that he was to leave a surviving witness, in Bryan Hartnell. He could have bragged endlessly about this crime, but in hindsight his failure to kill both victims actually played right into his hands. The detailed account of Bryan Hartnell, the description of the killer's costume and the extensive newspaper accounts, gave him all the publicity he could ever have wished for. What more was there to add. However, newspaper accounts were starved of the full details, in that the 'by knife' writing on the car door of Bryan Hartnell's car was withheld, probably to flush out the real killer from any subsequent hoaxers, and the Fairfield Letter may be one example.
Anybody who was aware of the Lake Berryessa attack could have concocted the phrase 'The Bleeding Knife of Zodiac', and more importantly its failure to highlight 'by knife' was an opportunity missed from a killer now determined to link himself to the authenticity of his correspondence, by enclosing the swatches of Paul Stine's shirt. The Zodiac Killer had his ego dented when his first cipher was cracked in a matter of days by schoolteacher Donald Gene Harden and his wife, Bettye June Harden, two amateur sleuths. His response was to send us the still unsolved 340 Cipher, crafted either with no solution or a solution that went far beyond simple homophonic substitution. The Fairfield Letter however, is a retrograde step into mediocrity, when the supposed Zodiac Killer now reverts back to scribbling nine symbols, showing little effort, in the apparent guise of a small code and beginning his letter with "I just want to tell you this state is in trouble, I will go for the government life", more reminiscent of a political agenda, with bold claims of another potential 38 victims. The 'knife' wording does look similar to the writing on the card door at Lake Berryessa, but the template for these letters was freely available throughout his correspondence up to this point. But he fails to corroborate this letter with a swatch of Paul Stine's shirt, why, because the real Zodiac Killer was to contact authorities just four days later.   

The Fairfield Letter was mailed on December 16th 1969, sandwiched between the Bus Bomb letter of November 9th and the Melvin Belli letter on December 20th and it was this reason, along with its design that has placed this relatively early letter into the section of unlikely Zodiac correspondence. The main reason for this centers on the belief that the Zodiac Killer, after murdering Paul Stine in Presidio Heights on October 11th 1969, actually mailed three pieces of Paul Stine's shirt to the newspapers, not two as is widely believed. This is not a new concept and there is a thorough section devoted to this on the excellent ZodiacKillerSite forum here, but for those who have not come across this, we shall do a brief summary, before bringing the Fairfield Letter into the equation.
It is widely acknowledged that two pieces of Paul Stine's shirt were sent, firstly to the San Francisco Chronicle on October 13th 1969, just two days after his murder and secondly on December 20th 1969 to the home residence of prominent attorney Melvin Belli, but it was likely a third piece was sent along with the '340 Cipher and Dripping Pen Card' on November 8th 1969 or Bus Bomb Letter a day later, outlined in two articles written by the San Francisco Chronicle and mentioned in a Youtube documentary. Anyone can believe in mistakes, but the wording in the Chronicle is specific, to say the least and the mailing of three portions of Paul Stine's shirt makes perfect sense, from photographs of the shirt on the Zodiac Killer Facts site marked A, B and C. 
Here is an excerpt from the FBI files (Zodiac 5 page 46/249), clearly showing three shirt pieces were mailed.