The most detailed description of the Zodiac Killer was presented in the days after the murder of Paul Stine in Presidio Heights, likely arrived upon by an amalgamation of two sets of eyewitnesses. The final age range estimated at between 35-45 years of age and semi-corroborated by Officer Donald Fouke, who described the suspect as 'graying in the rear' in his November 12th 1969 memorandum. The age of the killer may be relevant, when we consider the dramatic change in writing style from November 29th 1966/April 30th 1967 to the beginning of the Zodiac letters in 1969, just two years later. Is it possible to examine the linguistics from correspondence in the Cheri Jo Bates murder to the later writings and determine if they were authored by the same individual?  

The Zodiac Killer never bragged or labored the point about his four canonical attacks or five murders with respect to the victims. The closest he came was describing the attack on Michael Mageau, stating "When I fired the first shot at his head, he leaped backwards at the same time, thus spoiling my aim. He ended up on the back seat then the floor in back thashing out very violently with his legs; that's how I shot him in the knee."  But on this occasion he was prompted for more details about the crimes by Vallejo Police Chief Jack Stiltz, and duly responded. 
However, in the 'Confession' and Bates letters, just 2 to 3 years earlier, the author seemed to be relishing in the pain and misery he inflicted on Cheri Jo Bates and her family.
With statements such as "I said it was about time for her to die, she squirmed and shook as I chocked her and her lips twiched, and I then finished the job out cutting her throat," it had all the hallmarks of a killer who enjoyed reliving the events of that night, as well as exacerbating the heartbreak and suffering felt by family and friends. The author, not only named his victim in both letters, something the Zodiac Killer always steered away from, but he also mailed a letter to the father of the victim, Joseph Bates.
The addresses of the victims in the Zodiac crimes were routinely published in the newspapers, yet the Bay Area murderer failed to make contact with any of the victims families through mailed correspondence. The killer seemed to almost depersonalize the victims, only referring to them as kids, teenagers, boy, girl, woman, man, taxicab driver and people. When it came to his adversaries such as newspaper reporters, columnists, attorneys and police, then he had little problem naming Paul Avery, Marc H Spinelli, Herb Caen, Melvin Belli and David Toschi (depending on the validity of the correspondence).
Were the crimes simply his requirement to be taken seriously, so he could begin his letter writing campaign? In other words, they were not his primary focus, and why the attacks apparently ended after only 10 months.  

The most sexually explicit reference in the confirmed Zodiac letters was his statement of "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" in the deciphered 408 cryptogram. However, even this is downgrading sex below murder.
The 'Confession' letter is altogether different, referencing lying awake thinking about beautiful women, stating "Her breast felt very warm and firm under my hands, her lips twiched, keep your sisters, daughters and wives off the streets and alleys, I shall cut off her female parts and deposit them for the whole city to see and I am stalking your girls now." 
The emphasis of the letter is based solely on women, not couples, men or children. It also has a sexual component, not particularly evident in the Zodiac letters.
On March 13th 1971 the Zodiac Killer part-indicated his involvement in the Riverside murder of Cheri Jo Bates, but even then he couldn't refer to her by name - something he supposedly had no problem doing in both the Riverside correspondences a few years earlier. So, was the Riverside murderer really the Zodiac Killer?    ​

When Stephanie Guttman turned down the opportunity to accompany Cheri Jo Bates to the Riverside City College library on the afternoon of October 30th 1966, did she make alternative arrangements that ultimately led to her early demise. Despite entering the library to acquire her reading material shortly after opening time, she left within minutes. Nobody remembers seeing the young girl from 6:30 pm to 9.00 pm that evening, indicating she exited the library and went elsewhere. She wasn't murdered until approximately 10:30 pm that night, when screams were heard in the vicinity of the alleyway. At approximately 9:30 pm a female student purportedly noticed a man standing in the fateful alleyway smoking a cigarette and exchanged brief greetings with him. It is therefore clear that Cheri Jo Bates had been murdered subsequent to this encounter. 
The following observations take a new approach to the murder of Cheri Jo Bates, based upon the structure and wording of the 'Confession' letter mailed one month later. 

Everything contained in the 'Confession' letter was information readily available in the newspapers, however, this doesn't necessarily indicate that the author of the letter wasn't the killer. But there is a narrative in the letter that completely flies in the face of what was possible. The author of the 'Confession' letter described the middle wire of the distributor being pulled, the small knife and the cutting of the throat, which were all reported in the newspapers and totally correct, yet gave the impression that everything happened in one continuous timeline, which was impossible.
The impression given, is of a woman who enters the library while her vehicle is being disabled, and then exits to find her car won't start. The good Samaritan then offers her assistance and escorts her to a promise of a lift in his vehicle just down the street, before stabbing her. We know Cheri Jo Bates wasn't murdered between 6:00 pm and 9:30 pm, so why does the author cover all his bases in convincing the reader he is the killer, but fail so horribly with the timeline. 
Many details of the crime were printed in the newspapers, including an "awful scream between 10:15 pm and 10:45 pm and then a loud sound like an old car starting up." The author of the letter uses this scream in his letter, stating "she let out a scream once and I kicked her in the head," along with the presence of his vehicle: "I told her that my car was down the street and that I would give her a lift home."  However, if he knew she had exited the library to find her car disabled, then his story doesn't work from the standpoint of a 10:15 pm to 10:45 pm attack, as the library closed at 9:00 pm. Besides, he stated he followed her out of the library after about 2 minutes, and we know she left prior to 6:30 pm. Why is the author (if the killer) trying to give the impression that Cheri Jo Bates never left the campus that evening, when clearly her movements were unknown for approximately 4 hours. 
The author blatantly disregards the time of 10:15 pm and 10:45 pm in his continuous timeline, but certainly makes use of the scream and vehicle, to give us the impression he had killed Cheri Jo Bates moments after she exited the library. Does he weave his vehicle into the story to convince us he had to travel a reasonable distance to arrive near the alleyway, and therefore lives a reasonable distance away, when in actual fact he lived within walking distance of the Riverside campus.
If the author of the 'Confession' letter was the Zodiac Killer, he may have used this tactic nearly three years later, when using his vehicle as evidence he didn't live close to the payphone at Springs and Tuolumne after the attack at Blue Rock Springs.
If Cheri Jo Bates had left the library annex voluntarily before 6:30 pm and hooked up with somebody who lived nearby, who then escorted her back to her vehicle at around 10:30 pm, then the disabling of her vehicle could have taken place while she was present during an altercation. This would explain both windows rolled down, the right door being possibly ajar and the keys present in the ignition. A murder at approximately 10:30 pm with little passing traffic is an altogether more likely scenario, particularly when we consider the screams heard by eyewitnesses.
The author and killer would have been unaware at the point of writing, of a female student and man present in the alleyway with no body, and was desperate to shift the timeline 4 hours earlier, thereby ruling out any possibility of Cheri Jo Bates having ever left the campus to a nearby residence with somebody she knew. The use of his vehicle in the letter was the window dressing, to paint a completely different picture to the one that really happened that night - that Cheri Jo Bates was escorted from the campus on foot at around 6:30 pm by somebody she trusted. Somebody that would eventually betray that trust a mere 4 hours later.

The idea that the murderer of JonBenet Patricia Ramsey on 25/26th December 1996 would break into the Ramsey household, write a two and a half page ransom note using a notepad and pen found within the house (taking in excess of 22 minutes to compose), rather than write the note beforehand, and then not actually kidnap the young girl, but kill her in the basement, beggars belief.
Analysis of the note and the language contained within it, tends to indicate that it was written by a female.

Mr. Ramsey,
Listen carefully! We are a group of individuals that represent a small foreign faction. We do respect your bussiness but not the country that it serves. At this time we have your daughter in our posession. She is safe and unharmed and if you want her to see 1997, you must follow our instructions to the letter.
You will withdraw $118,000.00 from your account. $100,000 will be in $100 bills and the remaining $18,000 in $20 bills. Make sure that you bring an adequate size attache to the bank. When you get home you will put the money in a brown paper bag. I will call you between 8 and 10 am tomorrow to instruct you on delivery. The delivery will be exhausting so I advise you to be rested. If we monitor you getting the money early, we might call you early to arrange an earlier delivery of the money and hence a earlier delivery pick-up of your daughter.
Any deviation of my instructions will result in the immediate execution of your daughter. You will also be denied her remains for proper burial. The two gentlemen watching over your daughter do not particularly like you so I advise you not to provoke them. Speaking to anyone about your situation, such as Police, F.B.I., etc., will result in your daughter being beheaded. If we catch you talking to a stray dog, she dies. If you alert bank authorities, she dies. If the money is in any way marked or tampered with, she dies. You will be scanned for electronic devices and if any are found, she dies. You can try to deceive us but be warned that we are familiar with law enforcement countermeasures and tactics. You stand a 99% chance of killing your daughter if you try to out smart us. Follow our instructions and you stand a 100% chance of getting her back.
You and your family are under constant scrutiny as well as the authorities. Don't try to grow a brain John. You are not the only fat cat around so don't think that killing will be difficult. Don't underestimate us John. Use that good southern common sense of yours. It is up to you now John!
Victory!
S.B.T.C  Youtube.

This will be an exploration into the premise that the November 29th 1966 'Confession' letter, the Riverside 'Desktop Poem' and the three Bates letters were written by a female, consumed with hatred and jealousy towards her fellow womenfolk, and not by the murderer of Cheri Jo Bates, brutally stabbed and beaten in a Riverside alleyway on October 30th 1966.
Here is the wording contained within the typed 'Confession' letter:
​
She was young and beautiful. But now she is battered and dead. She is not the first and she will not be the last. I lay awake nights thinking about my next victon. May'be she will be the beautiful blond that babysits near the little store and walks down the dark alley each evening about seven. Maybe she will be the shapely blue eyed brunett that said xxx no when I asked her for a date in high school. But maybe it will not be either. But I shall cut off her female parts and deposit them for the whole city to see. So dont make it to easy for me. Keep your sisters, daughters and wives off the streets and alleys. Miss Bates was stupid. She went to the slaghter like a lamb. She did not put up a struggle. But I did. It was a ball. I first pulled the middle wire from the distributor. Then I waited for her in the library and followed her out after about two minutes. The battery must have been about dead by then. I then offered to help. She was then very willing to talk to me. I told her that my car was down the street and that I would give her a lift home. When we were away from the library walking, I said it was about time. She asked me "about time for what". I said it was about time for her to die. I grabbed her around the neck with my hand over her mouth and my other hand with a small knife at her throat. She went very willingly. Her breast felt very warm and firm under my hands. But only one thing was on my mind. Making her pay for all the brush offs that she had given me during the years prior. She died hard. She squirmed and shook as I chocked her. And her lips twiched. She let out a scream once and I kicked her in the head to shut her up. I plunged the knife into her and it broke. I then finished the job out cutting her throat. I am not sick. I am insane. But that will not stop the game. This letter should be published for all to read it. It just might save that girl in the alley. But that's up to you. It will be on your conscience. Not mine. Yes I did make that call to you also. It was just a warning. Beware....I am stalking your girls now.
CC.
Chief of Police Enterprise.

Although not wholly scientific, the wording from the 'Confession' letter was placed into two online tools to determine the gender of its author.
Textgain, a web service for predictive text analytics, predicted a female of 25 years or over, with 75% confidence.  
Hacker Factor, in formal genre, scored 849 for female and 428 for male, and a weak emphasis for European origin.
This analysis is not pushing the idea that the author of the Riverside communications was a female, simply considering it a possibility based on the language used- particularly within the 'Confession' letter and Riverside 'Desktop Poem'. 
The 'Confession' letter author appears to be reveling in the murder and demise of Cheri Jo Bates, a trait not exhibited by the Zodiac Killer, who, not only never mentioned his victims by name, but didn't dwell on the nature of the murders themselves. Here, the author is positively wallowing in the details of their achievement, opening with the lines "She was young and beautiful. But now she is battered and dead." In addition to being morally bankrupt, the author is going out of their way to exhibit a spiteful and malicious streak in the tone of the letter. Providing details of the crime to prove their connection to it, which they ultimately failed to do, appears of secondary importance to the author.  
Scouring any piece of text to discover the gender of its author is similar to handwriting comparison- it's subjective and dependent on the observer, and therefore cannot be scientifically validated. This is important to remember when reading the following observations.
Would a male individual have used the language contained within the 'Confession' letter? Just like the JonBenet Ramsey ransom note, the author appears to be selling a story- how "the shapely blue eyed brunett said no when I asked her for a date in high school" or maybe they will kill "the beautiful blond that babysits near the little store and walks down the dark alley each evening about seven." 
Phrases such as "the shapely blue eyed brunett," "the beautiful blond that babysits near the little store," "she went very willingly. Her breast felt very warm and firm under my hands," "keep your sisters, daughters and wives off the streets and alleys" and "it just might save that girl in the alley. But that's up to you. It will be on your conscience. Not mine" raises some questions as to the gender of the 'Confession' letter typist, who is adding superfluous detail into the story behind the murder of Cheri Jo Bates. In addition to this, making sure we understood that 'he' was rejected "by the shapely blue eyed brunett" and was "brushed off" by Cheri Jo Bates many times in 'his' pursuit of a heterosexual relationship. 
For those who believe a Riverside connection to the Zodiac Killer, another factor must be considered- despite the addresses of the Bay Area victims being widely publicized in the newspapers, not once did the Zodiac Killer write to the family members of the victims, such as David Faraday, Betty Lou Jensen and Darlene Ferrin, to name but three- as typified by the author of the Joseph Bates letter, in what can only be described as a cruel and unnecessary act.
The mailing of the Joseph Bates letter, again exemplified the callousness of an individual who seemingly bathed in the misery of the murder itself, something evidently absent from the Zodiac communications.
Are these observations, particularly regarding the 'Confession' letter, suggestive of a female author, or a male of effeminate tendencies or inadequacies who just got "brushed off." Or possibly a complete stranger. Your thoughts on either the 'Confession' letter or the JonBenet Ramsey ransom note would be welcome.      

Without a DNA or fingerprint connection apparently linking Riverside and the Zodiac Killer, many have tried to link the two through his correspondence. Was the Zodiac Killer responsible for the murder of Cheri Jo Bates in Riverside on October 30th 1966, and if so, was he a well-read individual with connections to the campus library.
David Oranchak of ZodiacKillerCiphers highlighted the text of Edward Hyde, Earl of Clarendon, present in the 408 Cipher, in his article entitled 'Throw the book at him, Part 3'. The section of text is from a book called 'The life of Edward, Earl of Clarendon, lord high chancellor of England: Volume 2':
​Forty-six consecutive letters from this text corresponds with a section of the 408 cipher. Dave Oranchak, the foremost expert on the Zodiac ciphers, commented on this "So, only one piece of text, from a vast collection of eleven billion pieces of text, fit into this chunk of cipher text. A one in eleven billion chance seems to suggest some significance. But don’t be fooled by this. Just because this rare event occurred, doesn’t mean it is anything more than a simple coincidence. If we didn’t already know the real solution to the 408, how do we know that this chunk of old and obscure text isn’t the correct solution?"  
I wanted to validate or refute whether this was a simple coincidence or not by examining whether the works of Edward, Earl of Clarendon featured anywhere else in Zodiac or Riverside correspondence. One wouldn't envisage many American criminals using the writings of a seventeenth century English statesman to form part of their serial murder exploits, and certainly not without access to a comprehensive library of books.
This is when I noticed another piece of obscure text from Edward, Earl of Clarendon and flew back to the last piece of notable text from the presumed Zodiac Killer on the Riverside desktop- the title of which was "sick of living/unwilling to die."  
One of Edward Hyde's quotes was “They who are most weary of life, and yet are most unwilling to die, are such who have lived to no purpose, — who have rather breathed than lived.” http://izquotes.com/quote/385232.
​Although not perfect, I couldn't help wondering if the Zodiac Killer was recalling from memory, as he did with 'The Mikado.'
Had he plagiarized "weary of life, unwilling to die" to "sick of living, unwilling to die," and would then later hide another section of Edward Hyde's text in the 408 cipher, as a form of link between the murder in Riverside and the Bay Area.
Edward Hyde, Earl of Clarendon was also an avid user of ciphers as revealed here in literary manuscripts; 
"Naturally a substantial portion of Clarendon's surviving manuscripts comprises his personal correspondence — both letters received by him from numerous correspondents and his own letters, written or signed by him, whether drafts, retained copies, or the letters actually sent. Among many notable examples are his letters written in August 1646 to William, Lord Widdrington, and to Sir John Berkeley, announcing the beginnings of his History of the Rebellion, and the letter he wrote on 12 November 1646, to Sir Edward Nicholas, describing his plan for the work and stating that he had already completed sixty sheets of it. Some of his letters, particularly those dating from the Civil War period, are wholly or partly in cipher or make use of pseudonyms in both salutations and signatures. The codes to sixteen such ciphers used by the Royalists are written out in Bodleian, MS Clarendon 94, and see also British Library,"
However, are there any alternatives to Edward Hyde- someone that possibly connects the 'Confession' letter and Riverside 'Desktop Poem' together, using the title of each communication.   

I have always believed the Zodiac Killer was driven by some form of warped religion- one that drove him to the confession box after each crime and manifested in the form of letters mailed to the newspapers and police.
Using the Riverside library as our primary focus once again, did the works of an early Christian theologian and philosopher influence the writings of Zodiac. 
'Peter A Fiore concludes that John Milton (an English poet, author of Paradise Lost, polemicist, man of letters, and civil servant for the Commonwealth of England) like many humanists, Christian philosophers, Reformers, and theologians of every variety in the early seventeenth century, drew widely from Augustine and that such indebtedness gave a richer and fuller theological dimension to his epic of lost paradise and enhanced the meaning of the poem.' 
link  
The Augustine he is referring to is St Augustine of Hippo (13 November 354 - 28 August 430), a Roman African, Christian theologian, whose writings influenced the development of Western Christianity and Western Philosophy. 
His work was translated by many individuals, but here are a few examples:
1] "Now is not the time for asking questions but for confessing to You. I was wretched, just as every mortal soul is wretched who is bound to the friendship of mortals. We are torn to pieces when we lose them, and so become aware of how wretched we were, even before we lost them. This is the way it was with me. I wept bitterly, and found rest only by weeping. I was so wretched that I held that life of wretchedness to be more dear to me than the friend for whom I wept. Even though I wanted to change it, I was more unwilling to lose it than I had been to lose my friend. Actually, I doubt that I would be willing to lose it even for him, as it is said of Orestes and Pylades, if that is true, that they would have gladly died for each other, or both died at the same time, rather than living part from each other. But I had begun to be afflicted with a strange kind of feeling, different from theirs. I cannot explain it, but I was tired of living and yet, I was afraid to die." link.​

2] "I do not know whether I would have been willing to die for him in the way that Orestes and Pylades, if the story is true, were willing to die together for each other. And yet a strange feeling had grown in me, and it was very different from theirs; I was sick and tired of living but I was too afraid to die." link.
​3] "But in me there was an odd kind of feeling, the exact opposite of theirs, for I was at once utterly weary of life and in great fear of death." link.
4] "I was at the same time thoroughly tired of living and extremely frightened of dying.”
link.
Was this a case of the Zodiac Killer recalling the literary work of another, as he did with the Gilbert and Sullivan Mikado, but paraphrasing it. However, in this instance, the author chose sick of living/unwilling to die as his title of the 'Desktop Poem'. 
On its own, this connection could appear a little unconvincing, but the author of the Riverside 'Desktop Poem' may have mailed correspondence to the Riverside Homicide Detail and Riverside Press Enterprise on November 29th 1966, in the form of letters entitled 'The Confession.'
Two weeks after the October 30th 1966 murder of Cheri Jo Bates, the Riverside Police staged a library reconstruction of the crime on November 13th 1966. The probable murderer then mailed the 'Confession' letters. St Augustine of Hippo wrote the Confessions (in which the above examples of text are contained), an autobiographical piece of work consisting of 13 books. "The Confessions of Saint Augustine in order to distinguish the book from other books with similar titles. Its original title was Confessions in Thirteen Books, and it was composed to be read out loud with each book being a complete unit.
Confessions is generally considered one of Augustine's most important texts. It is widely seen as the first Western autobiography ever written, and was an influential model for Christian writers throughout the Middle Ages. Professor Henry Chadwick wrote that Confessions will "always rank among the great masterpieces of western literature." link.  
St Augustine of Hippo was born on November 13th, the exact date of the library reconstruction. 
"The City of God Against the Pagans (Latin: De civitate Dei contra paganos), often called The City of God, is a book of Christian philosophy written in Latin by Augustine of Hippo in the early 5th century AD. The book was in response to allegations that Christianity brought about the decline of Rome and is considered one of Augustine's most important works, standing alongside The Confessions, The Enchiridion, On Christian Doctrine and On the Trinity. As a work of one of the most influential Church Fathers, The City of God is a cornerstone of Western thought, expounding on many profound questions of theology, such as the suffering of the righteous, the existence of evil, the conflict between free will and divine omniscience, and the doctrine of original sin."
"Shortly before Augustine's death, the Vandals, a Germanic tribe that had converted to Arianism, invaded Roman Africa. The Vandals besieged Hippo in the spring of 430, when Augustine entered his final illness. According to Possidius, one of the few miracles attributed to Augustine, the healing of an ill man, took place during the siege. According to Possidius, Augustine spent his final days in prayer and repentance, requesting that the penitential Psalms of David be hung on his walls so that he could read them. He directed that the library of the church in Hippo and all the books therein should be carefully preserved. He died on 28 August 430. Shortly after his death, the Vandals lifted the siege of Hippo, but they returned not long thereafter and burned the city. They destroyed all of it but Augustine's cathedral and library, which they left untouched."  Wikipedia.
​Was the murderer of Cheri Jo Bates somehow connected to the Riverside library, a well-read individual, who subtly introduced sections of text from St Augustine of Hippo into the titles of both the 'Riverside Desktop Poem' and 'The Confession' letter in order to give himself a feeling of superiority over the police and newspapers, as he would ultimately do several years later. 

"SICK OF LIVING, UNWILLING TO DIE" 

I have magnified the photographed version from the magazine and retyped it below. It almost concurs with the written version by the Argosy magazine. The original photographed version definitely states minutes not minuts, brunett as opposed to brownett, and victon as opposed to victim or victom.
​Up2something from Zodiac Killer Site forum pointed out that the 23rd line was not "I finished the job by cutting her throat" but "I finished the job out cutting her throat," don't on the 7th line was dont, "slaughter" was "slaghter" and "choaked her" was actually "chocked her". The words pertaining to each line is now correct in the photographed version retyped.. 

It has long been debated whether the 'Confession' letter sent on November 29th 1966 was the work of the Zodiac Killer.
In a recent History Channel docudrama about the Zodiac Killer, the typed 'Confession' letter was analyzed, looking for words that may connect the author of the Riverside correspondence with the infamous Zodiac Killer, focusing on words such as "twich" and "squirm". 
Here, we will go much further and analyze the readability level of the 'Confession' letter, and compare it with known Zodiac correspondence. The idea, is that even if the author of each correspondence was deliberately misspelling words or dumbing down the intellectual content in each letter, he should be consistently achieving the same readability level.
If there is some degree of correlation between the 'Confession' letter and the Zodiac correspondence, it may bolster the argument that the two cases are related- including the stabbing of Cheri Jo Bates and the Bay Area murders. 
The readability level of the above text has an average grade level of 17.04 and a median grade level of 16.40.
The November 29th 1966 'Confession' letter has average grade level of 3.80 and a median grade level of 3.97. 
These results were calculated using five tools: the Gunning fog index, the Flesch-Kincaid readability tests, the SMOG grade, the Coleman-Liau index and the Automated readability index. Here is a brief run down of each from Wikipedia and their respective link.

Gunning fog index: In linguistics, the Gunning fog index is a readability test for English writing. The index estimates the years of formal education a person needs to understand the text on the first reading. A fog index of 12 requires the reading level of a U.S. high school senior (around 18 years old). The test was developed by Robert Gunning, an American businessman, in 1952. The fog index is commonly used to confirm that text can be read easily by the intended audience. Texts for a wide audience generally need a fog index less than 12. Texts requiring near-universal understanding generally need an index less than 8.
Flesch-Kincaid readability tests: The Flesch–Kincaid readability tests are readability tests designed to indicate how difficult a passage in English is to understand. There are two tests, the Flesch Reading Ease, and the Flesch–Kincaid Grade Level. Although they use the same core measures (word length and sentence length), they have different weighting factors.
The results of the two tests correlate approximately inversely: a text with a comparatively high score on the Reading Ease test should have a lower score on the Grade-Level test. Rudolf Flesch devised the Reading Ease evaluation; somewhat later, he and J. Peter Kincaid developed the Grade Level evaluation for the United States Navy.
SMOG grade: The SMOG grade is a measure of readability that estimates the years of education needed to understand a piece of writing. SMOG is an acronym for Simple Measure of Gobbledygook. SMOG is widely used, particularly for checking health messages. The SMOG grade yields a 0.985 correlation with a standard error of 1.5159 grades with the grades of readers who had 100% comprehension of test materials. The formula for calculating the SMOG grade was developed by G. Harry McLaughlin as a more accurate and more easily calculated substitute for the Gunning fog index and published in 1969. To make calculating a text's readability as simple as possible an approximate formula was also given — count the words of three or more syllables in three 10-sentence samples, estimate the count's square root (from the nearest perfect square), and add 3.
Coleman-Liau index: The Coleman–Liau index is a readability test designed by Meri Coleman and T. L. Liau to gauge the understandability of a text. Like the Flesch–Kincaid Grade Level, Gunning fog index, SMOG index, and Automated Readability Index, its output approximates the U.S. grade level thought necessary to comprehend the text. Like the ARI but unlike most of the other indices, Coleman–Liau relies on characters instead of syllables per word. Although opinion varies on its accuracy as compared to the syllable/word and complex word indices, characters are more readily and accurately counted by computer programs than are syllables.
Automated readability index: The automated readability index (ARI) is a readability test for English texts, designed to gauge the understandability of a text. Like the Flesch–Kincaid grade level, Gunning fog index, SMOG index, Fry readability formula, and Coleman–Liau index, it produces an approximate representation of the US grade level needed to comprehend the text.

As another guide I used the text from the Coleman–Liau index above to generate an average grade level of 15.69 and a median grade level of 15.72. To check any section of text or the given examples, visit here. 
Here are the results:
The Confession letter 11/29/66 has average grade level of 3.80 and a median grade level of 3.97. 
The Riverside Desktop poem 1966 has average grade level of 3.89 and a median grade level of 4.00.
The San Francisco Chronicle 7/31/69 has average grade level of 8.15 and a median grade level of 8.12.
The Debut of Zodiac letter 8/4/69 has average grade level of 6.73 and a median grade level of 5.96.
The Paul Stine letter 10/13/69 has average grade level of 7.71 and a median grade level of 7.83.
The Bus Bomb letter 11/9/69 has average grade level of 8.56 and a median grade level of 8.69.
The Melvin Belli letter 12/20/69 has average grade level of 6.25 and a median grade level of 5.66.

The readability levels of the 1966 correspondence is notably lower than the initial Zodiac correspondence, although one has to factor in the near three year maturation of the subject, if indeed they are the same individual. But both are extremely low on the scale, indicating the Zodiac Killer and author of the 'Confession' letter were either extremely uneducated, or extremely accomplished at pretending to be uneducated. Whatever the case, there is a notable shift from 1966 to 1969.
​The above enlarged text has average grade level of 16.50 and a median grade level of 16.27, which highlights the difference in readability level the author in Riverside and northern California was operating at, either by intention or not.

https://charactercounttool.com/

It has long been believed the Zodiac Killer may have taken credit for crimes he never committed. One such example was the Modesto abduction of Kathleen Johns on March 22nd 1970, to which he claimed credit four months later, giving us details about the crime that had already been published in the newspapers. This may also have been the case in the murder of Cheri Jo Bates on October 30th 1966, when one month after the crime somebody sent typed Confession letters to Riverside Homicide Detail and the Riverside Press Enterprise on November 29th 1966. But were these from the killer, or an elaborate hoaxer.
When a person is manufacturing a story or crime they never committed they will obviously use material gleaned from the newspapers, but may subconsciously structure details in the letter in the same order they appeared in the newspaper. In addition, they may use identical or similar words used by the author of the article. The person may have attempted to present the Confession letter as first hand information but inadvertently leaked elements of the article into its wording and structure. Here is one such newspaper article released before the Confession letter arrived. 
'Riverside Police say their only clue in the brutal murder of a pretty, 18-year-old co-ed is a man's wristwatch found 10 feet from her slashed body. Officers speculated that while Cheri Jo Bates, a blonde cheerleader, studied Sunday night at the Riverside City College library, her killer disabled her car. Miss Bates' body, stabbed in the back, her throat slashed, was found early Monday under a tree, 100 feet from the car. The ignition key was in place in the compact car, but the distributor and coil wire had been torn loose, police said. Officers said an anonymous caller telephoned saying she had heard a terrified scream Sunday, then a muffled scream, then a car driving away The caller said she had not thought it serious enough to report until Monday.'              

Let us compare this article to the Confession letter, to view any similarities.
#1.The first thing the article details is the 'brutal murder of a pretty, 18-year-old co-ed', in addition to being a 'blonde cheerleader.' The Confession letter opens with 'she was young and beautiful', along with 'maybe she will be the beautiful blond that babysits,' or 'the shapely blue eyed brownett that said no when I asked for a date in high school.'
#2. The article then details the car being disabled. The Confession letter similarly switches to the Volkswagen Beetle, stating 'I first pulled the middle wire from the distributor', but the author retrieves some additional material from later in the article, where it states 'the distributor and coil wire had been torn loose.'
This topic of the 'middle wire' has been hotly debated in many forums, on whether the author of the Confession letter is supplying information only known to the killer. Here is some additional information to help you decide. "The ignition coil is the unit that takes your relatively weak battery power and turns it into a spark powerful enough to ignite fuel vapor. Inside a a traditional ignition coil are two coils of wire on top of each other. These coils are called windings. One winding is called the primary winding, the other is the secondary. The primary winding gets the juice together to make a spark and the secondary sends it out the door to the distributor.
You'll see three contacts on an ignition coil, unless it has an external plug, in which case the contacts are hidden inside the case. The large contact in the middle is where the coil wire goes (the wire that links the coil to the distributor cap." 
https://www.thoughtco.com/your-ignition-system-how-does-it-work
​http://www.1966vwbeetle.com/1966%20Wiring%20Diagram.htm
http://www.carparts.com/classroom/ignition.htm​​
 
#3. The article then mentions how Cheri Jo Bates was murdered: 'Miss Bates' body, stabbed in the back, her throat slashed, was found early Monday under a tree.'  
​The author of the Confession letter again follows: 'I grabbed her around the neck with my hand over her mouth and my other hand with a small knife at her throat,' continuing on to parrot the article 'I plunged the knife into her. Then I finished the job by cutting her throat.'  The article gives the impression Cheri Jo Bates suffered only two wounds, one to the back, one to the throat. The author of the Confession letter equally describes only two strikes with the knife, despite the fact Cheri Jo Bates suffered numerous lacerations to her body, over a prolonged period, and did not 'go to the slaughter like a lamb.'  
#4. The article then details an anonymous caller who 'had heard a terrified scream.'
The Confession letter again mimics this detail: 'She let out a scream once and I kicked her head to shut her up'. Triggered by the anonymous caller, the author of the Confession letter is reminded to state, 'Yes I did make that call to you also.'   

Finally, the author of the Confession letter stated "I first pulled the wire from the distributor. Then I waited for her in the library and followed her out after about two minuts. The battery must have been about dead by then. I then offered to help. She was then very willing to talk to me." None of which actually happened. 
Walter Siebert stated that 'he and a few friends were in the library from 7.15 pm until 9, but did not see Miss Bates, whom they all knew. They said they saw four men dressed in work clothes sitting on a fence across from the spot where Miss Bates' car was found, but they did not know them.'.
These workmen must have been spotted by Walter Siebert and his friends when they arrived at the library at 7.15 pm. The workmen said they saw Cheri Jo Bates by her Volkswagen Beetle, as they were sitting opposite her vehicle on the fence- but Cheri Jo was not recollected by Walter Siebert & Co that evening. We know that Cheri Jo Bates parked her Volkswagen Beetle on Terracina Drive no later than 6.15 pm, and it is assumed it remained there throughout until it was discovered disabled the following day. The four young men were interrogated by police, stating "they had seen Cheri Jo near her car the previous night". They must have seen Cheri Jo Bates at 6.15 pm when she parked up to enter the library. They do not mention to police anybody tampering with the Volkswagen Beetle, anybody assisting Cheri Jo Bates, or Cheri Jo Bates experiencing any car trouble. They fail to see anything suspicious, including hearing any commotion or screams from the alleyway. This totally negates the claims issued by the author of the Confession letter, and reinforces the idea the author is simply mimicking what they have read in the newspapers.
So was the author of the Confession letter the killer. I will let you decide.  

CHERI JO BATES-MINUTE BY MINUTE
CHERI JO BATES-MINUTE BY MINUTE [PT2]
​CHERI JO BATES-THE COMPLETE EYEWITNESS TIMELINE

The murder of Cheri Jo Bates outside the Riverside City College Library on October 30th 1966, may have been the day the Zodiac Killer under this moniker, started his campaign of terror. Although it would be at least one month before his typed 'Confession' letter surfaced with the threat of more to come. Five months later, on April 30th 1967, a further three letters sent to the Riverside Police, Riverside Press Enterprise and more chillingly Cheri Jo Bates father, suggested that this killer was not going to stop anytime soon.
His letters were signed off with what looked like a Z symbol, but as yet authorities were a long way from finding out, this may have been the very inception of the Zodiac, the 'calm' before the storm of Lake Herman Road and beyond.
What, if anything, lies within the Confession Letter to suggest this declaration of murder was in any way related to the other crimes that began on December 20th 1968, just over two years later.
It has been previously pointed out that the author of the 'Confession' letter used the wording "She squirmed and shook as I choaked her. And her lips twiched". This having striking similarities to the 'Little List' letter the Zodiac Killer mailed on July 26th 1970, in which he stated "Some I shall tie over ant hills and watch them scream + twich and squirm."
But more apparent is the egocentric nature displayed in the 'Confession' letter, that he maintains throughout his correspondence to the authorities, right through to the Exorcist Letter mailed on January 29th 1974, revealing character patterns of his own unique writing style. His extreme use of the word 'I' appears no less than 19 times, along with his use of 'me', 'my' or 'mine', a further 12 times in this short letter comprising of 423 words. So in total, a reference to himself appears 31 times. That is 7.33% or once every 14 words, and something we were going to get accustomed to over the following eight years.
The 'Bus Bomb' letter, 'Little List' letter and 'Melvin Belli' letter are further examples of the Zodiac Killer's compunction to constantly refer to himself as the focus of attention within his writings. In the Melvin Belli Letter this occurs 16 times, within the body of text containing 134 words, that is 11.94%. The Little List Letter contains 12 in 178 words, at 10.07% and the Bus Bomb Letter is equally high in frequency.   

In a previous article http://www.zodiacciphers.com/1/post/2013/10/the-phantom-murders.html , it was suggested that if the diagram at the foot of the Bus Bomb Letter, received one day after the Dripping Pen Card on November 9th 1969 was indicating murder sites. then by elimination there must have been two individual murders in August along the remaining lines shown  If so, then the Zodiac Killer was not claiming the Riverside attack on Cheri Jo Bates on October 30th 1966, despite part indicating its inclusion under the Zodiac banner, by signing off his Bates Letters on April 30th 1967 with a Z.  
However, if the Bus Bomb diagram was not referring to murder zones, then that leaves us another option for the months of December, July, August, September and October, indicated on the Dripping Pen Card.
The murders of Betty Lou Jensen and David Faraday in December, Darlene Ferrin in July, Cecelia Shepard in September and the murders of Paul Stine and Cheri Jo Bates, both in October, would now leave six murders of the seven accounted for and cementing the Riverside attack as a Zodiac crime. The seventh victim would still be, as yet undetermined. The Hood and Garcia murders would still remain a possibility, since they occurred on February 21st 1970, with the Domingos and Edwards murders on June 4th 1963 falling into the 'Pre-Zodiac' timeline, but not completely ruled out on this basis.
The Zodiac Killer in the 'Los Angeles' letter on March 13th 1971 claimed "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."
This may or may not be the case, but the murder of Cheri Jo Bates on October 30th 1966 is one crime, that in many respects has the hallmark of the Zodiac Killer stamped all over it.