When the Zodiac Killer mailed the second Fairfield letter on December 16th 1969 he included a very short code of five characters, accompanied by his Zodiac crosshairs, with four smaller crosshairs in each quadrant. It has been noted by many Zodiac researchers that this configuration resembled the Halloween card design he mailed approximately ten months later, which contained the bisecting "paradice" and "slaves", with the wording By Fire, By Gun, By Rope and By Knife in each quadrant. The rudimentary design of the Fairfield letter with four small crosshairs could be representative of these four weapons. I used this premise to place the word "By" immediately preceding the larger crosshairs, above ciphertext characters 4 & 5 (see below).

The last time the Zodiac Killer demanded we print his cipher in the newspaper, he wrote to the San Francisco Examiner and threatened "I want you to print this cipher on the frunt page by Fry afternoon Aug 1-69. If you do not print this cipher, I will go on a kill rampage Fry night". To the San Francisco Chronicle he wrote "If you do not print this cipher by the afternoon of Fry.1st of Aug 69, I will go on a kill ram-Page Fry. night". To the Vallejo Times-Herald he wrote "I want you to print this cipher on your frunt page by Fry Afternoon Aug 1-69, If you do not do this I will go on a kill ram page Fry night that will last the whole week end". Every single time the Zodiac Killer demanded the newspaper print his cipher, he followed it up by using "Fry" to represent Friday (six times in total). Therefore, when he demanded his five character code be printed in the newspaper by stating "you better print", it could be reasoned that this sentence be completed to "you better print Fry". This satisfies the repeating ciphertext character at positions 3 & 5.  

The Zodiologists website took a deep dive into the three Cheri Jo Bates letters mailed on April 30th 1967 and wrote "It can be reasonably assumed that the signature has a particular meaning beyond of just being a letter. If we should pick just one of the available options, we would say that the signature is a combination of the letter Z and the number 3. If it would be only the letter Z, there would be no need to write its top in flying-bird shape. The line at the bottom of the letter is straight. We also could not find a symbol that would resemble the signature. Therefore, we consider Z-3 as most plausible". 

​In the Confession letter, mailed on November 29th 1966, the author stated that Cheri Jo Bates was "not the first and she will not be the last", suggesting that the typist was claiming more than one victim. This conforms to the notion of a signature with an attached victim count, also displayed by the Zodiac Killer alongside his crosshairs in the numerous letters and cards he mailed. However, there is one communication that may have used a similar signature to that used in two of the Bates letters.

The Halloween card, mailed by the Zodiac Killer on October 27th 1970, gave us a victim count of "14" on the skeleton's hand, and fashioned the number fourteen as "4-TEEN", using the number "4" to express the word "four". The Zodiac Killer may have used the same tactic with the symbol on the envelope and card inner, using 4 dots to indicate that the "F" stood for "fourteen" rather then "fifteen". If the symbol on the Halloween card inner and outer denoted a victim count for a third time, we have the possibility of a joined "Z" and "F" denoting the fourteen victims claimed by the killer - extremely similar to the joined "Z" and "3" suggested by the Zodiologists website. If this hypothesis is true, it could indicate a common thread from Riverside to the Bay Area through the correspondence of a killer. It must also be noted that the Halloween card was the only confirmed communication to use the letter "Z" to denote the "Zodiac" pseudonym - and it used the letter "Z" twice - just like the two Bates letters (if you believe the premise). The Zodiac Killer also used the word "BY" in prominent positions four times within the Halloween card, mirroring the "BY" which headed both Confession letters. The use of a Halloween card to convey these similarities is pertinent to the fact that the body of Cheri Jo Bates was discovered on Halloween morning  

The Zodiac's Little List letter (July 26th 1970), believed by some to be the previous communication to the Halloween card, began his little list by misspelling "victim" to "victom", and wrote. "Some I shall tie over ant hills and watch them scream + twich and sqwirm". The Confession letter author began his little list by using the misspelling "victom", before typing "She squirmed and shook as I chocked her, and her lips twiched. She let out a scream once". The author of the Confession letter had a smaller list, but included "the beautiful blond that babysits near the little store" and "the shapely blue eyed brunett that said no when I asked her for a date". The Zodiac Killer could have fashioned the Little List letter and Halloween card to make journalists and/or law enforcement draw the conclusion he was responsible for the murder of Cheri Jo Bates in Riverside on October 30th 1966. This ultimately became the case, when Paul Avery presented the link in the San Francisco Chronicle on November 16th 1970, much to the dismay of law enforcement. 

The information regarding the Confession letters was readily available to the Zodiac Killer, when the Inside Detective magazine published a comprehensive article about Cheri Jo Bates in January 1969. However, the signature on two of the Bates' letters had not been published in the newspapers or magazines prior to October 27th 1970, making the possibility of two "Z's" and a victim count, deployed in Riverside and the Bay Area, through three communications and one killer, a viable proposition. If Riverside really was the Zodiac Killer, had he reset his victim total when switching from "Z" to the "Zodiac" pseudonym, beginning anew some 450 miles north? 

It could be argued that the author of the Scorpion letters, which were mailed to John Walsh, presenter of the popular television show America's Most Wanted, was hinting he was once the infamous Zodiac Killer. In a series of cryptograms and letters sent in 1991, the headline text of "Hi, Remember Me" is fairly self-explanatory (see below). The wording used in the correspondence such as "you and your over anxious associates would try and nail me even if I used a P.O. Box for a return address" is interesting, because post office box keys were a feature of the Eureka card just a few months earlier, in 1990. The Atlanta letter, almost certainly mailed by the Zodiac Killer on March 8th 1981, contained the wording "I am not writing in the same hand writing". The Scorpion letters author wrote "My style of hand writing on these cards is very much altered". There is a distinct gap between "hand" and "writing" in both instances (rather than "handwriting" written as one word). The Scorpion letter also stated "I will soon start collecting bodies for you", replacing the word "slaves" used by the Zodiac Killer. 

These complex cryptograms are extremely difficult to solve because of the excessive ciphertext characters used in the encoding process. However, there are some possible openings. The Zodiac Killer mailed a 408 character cipher on July 31st 1969, a 340 character cipher on November 8th 1969, a 38 character cipher on December 7th 1969, a 13 character code on April 20th 1970 and a 32 character code on June 26th 1970, but not once did he use the "sun cross" or "number 7" as a ciphertext character. The 148 character cipher mailed to the San Francisco Chronicle by the Zodiac Killer sometime in May 1971, the 50 character cipher mailed to the Albany Times Union newspaper on August 1st 1973, and the 180 character Scorpion cipher mailed in 1991 (all bearing traits of the Zodiac Killer and not contemporarily published in the newspapers), all contained the "sun cross" and "number 7" as a ciphertext character. ​The "number 7" in the 1971 and 1973 ciphers, both decoded to the plaintext letter "A".

In the 148 character cipher mailed in 1971, the Zodiac Killer used the "sun cross" as a signature rather than his traditional crosshairs - thereby signing off his communication with the letter "Z" - because the "sun cross" descoded to the plaintext letter "Z" in the 148 character cipher. Bearing in mind that the Scorpion letter author headlined with the wording "Hi, Remember Me", it had to be considered that the pseudonym "Zodiac" may have been hidden somewhere in the cryptogram. Since the Zodiac Killer probably used the "sun cross" to represent the letter "Z" in the 148 character cipher, I took a look at the 180 character Scorpion cipher to see if any repeating ciphertext characters would mimic the pseudonym "Zodiac", using the "sun cross" to represent the plaintext letter "Z". Below are the examples I found beginning on row 2 and 14. To view the Scorpion letters and ciphers, please visit Science Blogs. 

Recently I have been covering the autopsy reports of various Zodiac Killer victims to better understand the dynamics of each crime - and as such - dispel some of the inaccuracies and myths surrounding the four canonical attacks. The final Zodiac murder of Paul Stine in Presidio Heights on October 11th 1969 will be examined using information taken from the autopsy report featured on the once Howard Davis website. Here is an excerpt taken from the coroner's findings; "Both lungs are moderately increased in weight. There is congestion at the base and dependant portions. Multiple intraparenchymal hemorrhages are noted". Lung parenchyma is the substance of the lung that is involved with ​gas exchange and includes the pulmonary alveoli.

If Paul Stine was of healthy disposition and had no underlying health issues, the multiple parenchymal hemorrhages causing blood to leak into the tissues of the lungs and creating congestion in the dependent portions, can be found in patients with chest trauma. An impact to the chest from such things as the steering wheel can cause parenchymal hemorrhage without injury to the sternum and ribs. "A pulmonary contusion is a bruise on the lung parenchyma. Pulmonary contusion is reported to be present in 23% of patients with significant blunt chest trauma, and occurs most often from automobile collisions with rapid deceleration. Regardless of the mechanism, injury to the lung results in injury to capillaries and the leaking of blood into the lung tissue and alveoli. This collection of fluid in the alveoli interferes with normal alveolar-capillary gas exchange". link. "Chest wall and pulmonary injuries caused by blunt thoracic trauma include many organs, tissues and systems. The age of the patient is important when evaluating a blunt chest trauma. While a trauma in the pediatric age group may not cause a chest wall injury due to bone elasticity, it may lead to serious complications and even death in the elderly population.The best example of acceleration-deceleration damage is motor vehicle accident. The most common condition is the sudden and high-speed deceleration of the anterior thorax, resulting in injury to the vascular structures, bones, soft tissues and organs. At the same time, the presence of steering wheel deformity caused by the driver hitting the steering wheel increases thoracic injuries, complications and mortality" .link..

"Signs and symptoms of thoracic trauma include: cyanosis of fingers, lips or face, dispnea, tachpnea or bradipnea and contusion". link. Cyanosis is the medical term for a blue, purplish or gray discoloration of the skin, caused by a shortage of oxygen in the blood. Peripheral cyanosis can occur in the extremities such as the hands, fingers and toes. Paul Stine had, according to the coroner, parenchymal hemorrhage in the lungs (reducing oxygen levels in the blood) and dark marks on the dorsal side of his left hand. It is not possible to conclude whether the two conditions are related to one another, but these autopsy findings of blood in the tissue of both lungs is an unusual facet of this case. If the Zodiac Killer had presented the gun earlier in Paul Stine's journey, could the taxicab driver have attempted rapid braking in an attempt to disarm his eventual killer, causing non-fatal steering wheel trauma to his anterior chest region, and causing the Zodiac Killer to strike his legs on the rear of the front seat? Officer Donald Fouke did describe the Zodiac Killer as walking with a "lumbering gait" and "stumbling along like a semi-limp" in the 2007 Zodiac documentary. But how accurate are these recollections 38 years subsequent to the events that night?

It is without doubt that Paul Stine died as a result of one shot to the right side of his head causing massive brain injury, but what occurred during the taxicab journey from the Union Square plaza in San Francisco to the intersection of Washington and Cherry Streets in Presidio Heights? It is unknown when the Zodiac Killer pulled the gun on Paul Stine, despite the common portrayal of a surprise attack occurring during the very last seconds of the trip.​

The injury to Paul Stine's head was described upon opening the cranium as "a small quantity of hemorrhage into the temporal muscles bilaterally. There is extensive fracturing of the base of the skull. The above described entry wound has passed almost directly medially, passing beneath the pituitary gland and sella turcica, the floor of the left orbit and into the midportion of the left temporalis muscle near the zygomatic arch (red circle on diagram)..​A smashed and fragmented, copper jacketed lead bullet is found embedded in the left temporalis muscle. There is laceration of the ventral surface of the right temporal lobe. There is marked flattening of the gyri and diffuse hemorrhage into the subarachnoid space".

To sum up the autopsy, the bullet entered just in front of the right ear, traveled at a shallow angle anteriorally and struck the left temporalis muscle (used in chewing). Without knowing the head position of Paul Stine at the moment the gun was fired, makes it impossible to determine where the killer was seated in the taxicab when he delivered the fatal shot. The parenchymal hemorrhages to the lungs of Paul Stine (if not present prior to the taxicab journey) warrants an answer to the possible events that occurred within the taxicab during his final journey on October 11th 1969. The story is not complete.