The Zodiac Killer mailed the 'Button' letter and Phillips 66 Map on June 26th 1970 overlaying his crosshairs over Mount Diablo. Just a month later, realizing the clues in the Button letter were insufficient, he gave us the answer in the 'Little List' letter declaring "PS. The Mt. Diablo Code concerns Radians & # inches along the radians". The crosshairs with the bold SFPD = 0 were telling us exactly where he planned to 'set his bomb'. By identifying the location in degrees, using a black, bold circle and coupling it with a 'dig' at the San Francisco Police Department, he was effectively giving us the target and the location. His target was the San Francisco Police Department subtended at an angle of 246 degrees from true north. Bearing in mind his bomb threats were focused in San Francisco, all we had to do was find the police department. How experienced the Zodiac Killer was regarding radians is unknown, but he designed a form of clock face with a directional marker pointing true north and then stated "0 is to be set to Mag.N" (which was approximately 17 degrees in 1970). We don't actually need to know how many radians he intended, from which point, and whether they were meant to travel clockwise or anticlockwise around the clock face, because the bold, dark circle is already the answer.   

On the left I have combined the crosshairs from the 'Button' and 'Little List' letters. The bold, dark circle is 246 degrees around the circumference (which is 4 radians + magnetic north). A radian is 57.3 degrees, so 4 X 57.3 + 17 degrees = 246 degrees. If we deduct 2 radians from true north we get 360 - 114.6 = 245.4 degrees. So, whether we use 2 radians anticlockwise from true north or 4 radians clockwise from magnetic north, the result falls within the circumference of his bold, dark circle (246 and 245.4 degrees). 

Drawing a line through this bold, dark circle from Mount Diablo and across San Francisco, it passes near only one police station, that of Ingleside. It isn't absolutely accurate, but it is the closest police station the measurement relates to. This is why he added SFPD next to the bold, dark circle rather than placing it at the foot of his letter in customary fashion. His bomb was to be set in the vicinity of the San Francisco Police Department at Ingleside. Whether he actually meant it is debatable, but it was the threat that was likely his main goal - sowing more fear into the heart of San Francisco.

The Zodiac Killer made many bomb threats in the 1970s, including references to "black power" in the April 28th 1970 'Dragon' card, along with his Symbionese Liberation Army letter in 1974. This has led some to ponder if the Zodiac Killer was somehow affiliated to a radical group, or possibly infuriated by groups such as the Black Liberation Army or Black Panthers, stealing the limelight away from his dwindling publicity: "I would like to see some nice Zodiac buttons wandering about town. Everyone else has these buttons like, black power, melvin eats bluber, etc". The Zodiac Killer may have been mailing correspondence well into 1971, with communications such as the July 13th 1971 'Monticello' card, 148 character cipher, and quite possibly, the unseen DMV letter. At this period of time, it appeared as though the Zodiac Killer was desperately attempting to connect himself to the murders of Debra Gaye Furlong, Kathy Ann Snoozy and Kathy Bilek, all savagely stabbed in excess of fifty times.   

Mary Alice Willey arrived in San Francisco in 1969, making some questionable alliances, including the black power movement. "She became a strident devotee of George Jackson, the charismatic but militant San Quentin inmate who had gained international fame for his best-selling prison classic, "Soledad Brother." She wrote letters to Black Panther Johnny Spain, who was also incarcerated at San Quentin. And she began associating with members of the Black Liberation Army, a violent offshoot of the Black Panthers that would become implicated in the Aug. 29, 1971, killing of a police officer at San Francisco's Ingleside Station. There is reason to believe that Mary Alice may have played a role in the attack and the slaying of Sgt. John V. Young". Read more at the San Francisco Chronicle. 

While in San Francisco she dated a fellow student, Patrick Warren McDowell, who claimed he belonged to the Symbionese Liberation Army, a group ultimately responsible for the kidnapping of Patty Hearst in 1974. In February 1971 he was arrested for the failed robbery of the Sugar Bowl Ski Lodge near Lake Tahoe, having borrowed Mary Alice Willey's car.

If the Zodiac Killer was still closely following the news in 1971, as it appears he was, regarding Snoozy, Furlong and Bilek, then it wouldn't have gone unnoticed that the Ingleside Police Station he had threatened to bomb just over a year ago, had now come under attack. On August 21st 1971 a gun was smuggled to George Jackson in San Quentin Prison. As Jackson was being escorted back to his jail cell, a guard noticed the gun. Jackson raised the weapon and, paraphrasing Vietnamese revolutionary leader Ho Chi Minh, declared: "This is it, gentlemen. The dragon has come." As he later ran across the prison courtyard, a guard opened fire killing Jackson instantly. 

On August 29th 1971, a woman who bore a resemblance to Mary Ann Willey, wearing a blond wig, entered Ingleside Police Station to report a stolen purse. "Police have long thought the woman who had come to the station to report her stolen purse was a lookout connected to the Black Liberation Army, and they believed that woman was Mary Alice". Chronicle.  A short time later several black men entered the station and murdered John V. Young with a shotgun through the grill of the reception desk. Within two weeks of this attack Mary Alice Willey had vanished. 

On September 11th 1971 a worker stumbled across the body of a woman while driving along the Delta-Mendota Canal in Stanislaus County near Patterson - close to the abduction site of Kathleen Johns on March 22nd 1970. There was no evidence of sexual assault, but she had been stabbed at least 65 times, and her murderer had attempted to sever her fingers and hands. An identification was not made. 

"In March 1970, a pregnant woman and her 10-month-old daughter were abducted near Modesto by a man who drove them around the valley and, according to some police reports, threatened to kill them. Kathleen Johns and her daughter ultimately escaped and hitched a ride to the police station in Patterson. While giving her statement, Johns reportedly saw a drawing of the Zodiac Killer and claimed he was the one who abducted them.

Johns' conflicting statements, though, cast doubt upon whether she had, indeed, encountered and survived the Zodiac. The murder Hedrick is revisiting happened just 18 months after that abduction. The Zodiac claimed 37 kills, though only the five were confirmed. There's nothing to suggest the Zodiac Killer, who never was captured, claimed credit for this murder, sheriff's Detective Marc Nuno said". Read more at The Modesto Bee.

Nearly four decades later, in September 2008, her body was exhumed from Patterson cemetery, and using a forensic sculptor to reconstruct her face and modern DNA testing, she was finally identified as Mary Alice Willey.​

The Zodiac Killer gave us a map code on June 26th 1970, stating the "map coupled with this code will tell you where the bomb is set." To this day no bomb has been unearthed and the threat was likely an idle one, designed primarily to create fear within the American community. However, the map and code were real, and the answer to both has probably been sitting in plain sight for nearly fifty years. The Zodiac, aware that the '32 Symbol' cipher was unable to be broken because it had 29 different characters, gave us all the answers one month later when he mailed the July 26th 1970 'Little List' letter.
The numerous suggested bomb threats were all mailed to the San Francisco Chronicle, so it was evident that his threats were focused on San Francisco itself - which is why the Mount Diablo map included San Francisco and Vicinity rather than just the area around Mount Diablo. The 'Little List' letter was replete with all the information required to crack his map code.
In the 'Button Map and Code' letter the author gave us the "map coupled with this code will tell you where the bomb is set," and just one month later, clearly told us that the code "concerns Radians & # inches along the radians" Therefore, the code will at least contain the words "radians" and "inches" in the answer - and that may very well be the case. In fact, it tells us exactly where the intended bomb was to be set, within the design of the crosshairs with the bold black circle. With the threats geared towards schoolchildren and police it is apparent that these are the likely targets. The reference to SFPD = 0 being incorporated within the crosshairs, along with an accentuated black, bold zero suggesting a location, should be the biggest clue of all. His intended target was the San Francisco Police Department - the location of which can be found within this bold circle. 
The Zodiac Killer referenced "radians" and "inches" (not parts of radians and inches), so with probably just the use of a ruler back in 1970 the Zodiac Killer would measure his intended target this way. Therefore, if he is one eighth of an inch off in his measurements we can forgive him this textual indiscretion. Fortunately, we have Google maps, so the task is much easier.
With an intended target in San Francisco, there is only one answer possible to the "radians" and "inches" conundrum, and it's governed by geography. 1 radian = 57.3 degrees, 2 radians = 114.6 degrees, 3 radians = 171.9 degrees, 4 radians = 229.2 degrees and 5 radians = 286.5 degrees. This is detailed crudely on the map below.
It is apparent that Zodiac wasn't referring to 5 radians, as a line subtended from Mount Diablo at this angle would pass north of San Francisco. The same applies to 3 radians which runs parallel to San Francisco. Therefore, the answer has to be 4 radians or 229.2 degrees. The lines drawn below are only approximations, so are not pinpoint. 4 radians or 229.2 degrees passes over San Francisco somewhere in the vicinity of the airport - but this isn't the answer. If we add back the magnetic north value of 17 degrees in 1970, it equals 246.2 degrees. After all, Zodiac stated on the map, it was "to be set to Mag.N." 
How do we know 246.2 degrees is the correct angle to be subtended from Mount Diablo? The answer is simple - Zodiac told us so. Place the crosshairs above over a compass rose. A line subtended from the center of the compass rose passes exactly through the center of the bold black circle. In other words, the bold black circle is positioned at 246.2 degrees around the crosshairs. This is 4 radians + 17 degrees (magnetic north). Now all we have to do is find the inches subtended along the 246.2 degree line. This is even easier.     

The map scale is 6.4 miles to the inch, so the geography of San Francisco is self-constraining.
It is approximately 26.5 miles to the eastern edge of San Francisco from Mount Diablo (using the angle of 246.2 degrees).
4 inches would equal 25.6 miles, therefore, 4 inches subtended from Mount Diablo would land in the sea. Unless the Zodiac Killer had a submarine to bury his bomb this is not very likely.
It is approximately 34 miles to the western edge of San Francisco from Mount Diablo (using the angle of 246.2 degrees). 
6 inches would equal 38.4 miles and again would land in the sea.
Therefore, the answer has to be five inches along the 4th radian (plus magnetic north of 17 degrees). If this lands over the San Francisco Police Department we are in business. But first, we shall fill in the '32 Symbol' code using the words or clue given by the Zodiac Killer in the July 26th 1970 'Little List' letter.  
The section below is almost the complete solution to the '32 Symbol' cipher. Note how the Zodiac Killer inserts a hashtag style character between the "&" and "inches", with an arrow pointing between these two pieces of text. He is telling us to insert something here. We know from the above calculation it must be five inches, thereby completing the phrase:
"P.S The Mt.Diablo code concerns Radians & five inches along the radians"
​

The Zodiac Killer wasn't totally accurate, because the phrase should have read "P.S The Mt.Diablo code concerns Radians & five inches along the radian". The five inches to be subtended along the 4th radian (plus magnetic north) = 246.2 degrees. 
There are only three repeating characters in the code below, the triangle, the letter C and the letter O. With the inserted solution, these three characters are now represented by R, A, N, N, E and N. 

It was there in the Zodiac Killer's words all along; "The Mt.Diablo code concerns...... Radians & inches along the radian"
The last thing we have to do is place the large crosshairs with the black circle over the map of Mount Diablo, San Francisco and Vicinity. The location where the intended bomb was to be set should be 246.2 degrees and 5 inches subtended along a line drawn from Mount Diablo. It should also land over something to do with the San Francisco Police Department. Bearing in mind this was 1970 and the Zodiac Killer was using a ruler over a map, one eighth of an inch or so would be an acceptable margin of error, based on a map scale of 6.4 miles to the inch. The center and style of the black bold circle may be representative of a designer who intended the target to fall within this circle.  
There was no room on the map below, but we can see that if the superimposed crosshairs were expanded over the city of San Francisco, the center of the bold black circle subtended at 246.2 degrees for 5 inches would fall over the San Francisco Police Department at Ingleside Station. 
Ingleside Police Station is 31.06 miles from Mount Diablo. There are 6.4 miles to the inch. So Ingleside is 4.85 inches along the subtended angle of 246.2 degrees. Allowing for the leeway of crude measurement, this is 97% accurate in respect to 5 inches over the distance involved. This is why the Zodiac Killer placed SFPD next to the bold circle - it represented zero in mocking fashion, but more crucially, it represented the location of where the bomb was intended to be set - Ingleside Station or somewhere close by.              

Richard Radetich, the fallen officer, possibly referred to in the Zodiac Killer 'Button' letter was initially assigned to Ingleside Police Station, before moving to Park Station and eventually to Accident Investigation.

Footnote: What level of understanding the Zodiac Killer had regarding the concept of radians is unknown, but they are a counterclockwise value around the circumference of a circle. He placed his crosshairs over Mount Diablo, to which he added a sort of clock face, replacing the number twelve with a zero, stating it was "to be set to Mag.N". It can be shown that 4 radians and Magnetic North will fall within the bold, black circle he placed on his 'Little List' crosshairs. In addition, it can be shown that traveling 2 radians counterclockwise from True North will again fall within the bold, black circle. The use of the clock face and the directional north marker set at zero, may indicate that Zodiac intended this as his starting point for any calculations. The mere fact that the above measurements, either clockwise or counterclockwise, using whole radians, both fall inside the black circle, would seem to suggest that the 246 degree angle subtended from Mount Diablo over San Francisco is where we should be looking.​

The Zodiac Killer quoted a portion from one of the three stanzas of The Mikado's Tit-Willow, when he mailed the 'Exorcist' letter on January 29th 1974. This may possibly have been the third correspondence, including the 'Halloween' card, where The Mikado was referenced. The Zodiac Killer began with the 'Little List' letter on July 26th 1970, in which he paraphrased 'As some day it may happen' featuring Ko-Ko the Lord High Executioner. In the letter he was effectively quoting the search for future victims as paralleling his agenda throughout the state of California. If we break down the 'Exorcist' letter into its constituent parts, it becomes apparent the correspondence is a further threat towards the citizens of California rather than a declaration of his impending suicide.
If we take a look at the October 27th 1970 'Halloween' card and compare it to his confirmed attacks, only one stands out. On September 27th 1969 Cecelia Shepard and Bryan Hartnell were relaxing by the shores of Lake Berryessa when a man spotted by Cecelia ducked behind a tree to don an executioner's mask and waistline bib. This theatrical entrance in the form of Ko-Ko the Lord High Executioner has long been suggested as an influence on the Zodiac's actions and writings. Here is an extract from the San Francisco Chronicle on October 12th 1970, just 15 days prior to the mailing of the 'Halloween' card:
"It was immediately apparent that Zodiac had plagiarized several stanzas from an aria in the Gilbert and Sullivan operetta 'The Mikado'. It is the entrance aria of Ko-Ko, the Lord High Executioner. A quiet search of onetime Ko-Ko's has turned up none that could be Zodiac. Obvious differences in physical description and handwriting comparisons have cleared all Ko-Ko's tracked down since the arrival of the July 27 letters." 

The 'Halloween' card depicted an eye peering from the knothole of a tree, accompanied by the words 'peek-a-boo you are doomed', implying the impending threat of the Zodiac Killer hiding behind the tree at Lake Berryessa and his ultimate arrival bedecked in an executioner's outfit. If you look up the definition of peek-a-boo in Wikipedia, it quotes "Peekaboo (also spelled peek-a-boo) is a form of play primarily played with an infant. To play, one player hides their face, pops back into the view of the other, and says Peekaboo!, sometimes followed by I see you! There are many variations: for example, where trees are involved, "Hiding behind that tree!" is sometimes added." 
However, Peek-A- Boo was also a character in another version of The Mikado at around the same time as the Gilbert and Sullivan operetta. "In 1888 Jack the Ripper terrorized the Whitechapel district of London. In the same year of somewhat less significance Ed J. Smith wrote a stage parody called The Capitalist; or, The City of Fort Worth. Designed to encourage capital investment in Fort Worth, Texas, and underwritten by local banks and railroad lines, the two act piece features characters named Yankee-Doo, Kokonut, By-Gum and Peek-A-Boo." Here is an image depicting this reference.     

Peep-bo is the English version of peek-a-boo, and has a curious, albeit likely unintentional connection to the Lake Berryessa murder of Cecelia Shepard, in the nursery rhyme Little Bo-Peep.
​"The earliest record of this rhyme is in a manuscript of around 1805, which contains only the first verse. There are references to a children's game called "bo-peep", from the 16th century, including one in Shakespeare's King Lear (Act I Scene iv), for which "bo-peep" is thought to refer to the children's game of peek-a-boo, but no evidence that the rhyme existed earlier than the 18th century. The additional verses are first recorded in the earliest printed version in a version of Gammer Gurton's Garland or The Nursery Parnassus in 1810". Wikipedia.
Peep-bo was one of the three little maids from The Mikado: "Three little maids from school are we, pert as a school-girl well can be, filled to the brim with girlish glee, three little maids from school." 

Three young girls from Pacific Union College would feature in the Zodiac story of Lake Berryessa that day, when describing a suspicious individual roaming the hillsides surrounding the lake- later providing a sketch of the individual. 
Little Bo-Peep was a shepherdess, so its significance to the name of Cecelia Shepard could not be ignored, although likely accidental. "She heaved a sigh and wiped her eye, and over the hillocks went rambling, and tried what she could, as a shepherdess should, to tack each again to its lambkin"
The Riverside murder of Cheri Jo Bates on October 30th 1966 and the subsequent 'Confession' letter held an odd precursor to the events of Lake Berryessa, when it stated "Miss Bates was stupid. She went to the slaughter like a lamb", along with the widely referenced "She squirmed and shook as I choked her, and her lips twitched" connection to the 'Little List' letter.  

​The Zodiac Killer, after mailing his response to the unearthed Riverside connection would then go into hibernation from March 13th 1971 until the arrival of the 'Exorcist' letter nearly three years later on January 29th 1974, leading many to believe the Zodiac Killer was likely incarcerated during this period. 
"Taken from the county jail
By a set of curious chances;
Liberated then on bail,
On my own recognizances;
Wafted by a favouring gale
As one sometimes is in trances,
To a height that few can scale."  Behold the Lord High Executioner Youtube
The Mikado/Act I/Part V
The Lord High Executioner was to return, berating the 1973 film 'The Exorcist,' yet curiously comparing it to the Gilbert and Sullivan's satirical operatic comedy, The Mikado, calling it "the best satirical comedy that I have ever seen."  He then signed his name using the verse of Tit-Willow by Ko-Ko: "He plunged himself into the billowy wave and an echo arose from the suicides grave, titwillo, titwillo, titwillo."
The whole letter was effectively announcing the return of the Lord High Executioner after nearly three years. Here is the 'Exorcist' letter broken down into its constituent parts to reveal its likely meaning.
"I saw and think "The Exorcist" was the best satirical comedy that I have ever seen, even better than The Mikado. Signed, yours truley: The Lord High Executioner. If I do not see this note in your paper, I will do something nasty, which you know I'm capable of doing- To Kill."
Kevin Robert Brooks came up with possibly the best interpretation of the Japanese/Asian symbols at the foot of the letter, befitting of Ko-Ko the Lord High Executioner. The "This is the Zodiac speaking" introduction was apparent by its absence, as well as the Zodiac crosshairs- but the Lord High Executioner was alive and well, and still making threats.  

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

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

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

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

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

In analyzing the 'Button' letter map and code mailed on June 26th 1970, it is imperative we take a close look at the Zodiac Killer correspondence in the preceding few months to this communication for any clues to his mindset and intentions. There will be no definitive solution to the 32 symbol code presented here, although a location for where his bomb was 'to be set' can be argued with confidence, using four pieces of Zodiac material.
On April 20th 1970 the killer mailed 'The My Name is..Cipher' and stated "I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station.  Even though I talked about killing school children with one. It just wouldn't doo to move in on someone else's teritory.  But there is more glory in killing a cop than a cid because a cop can shoot back." The Zodiac Killer was referring to the murder of San Francisco police officer Brian McDonnell on February 16th 1970, two months earlier, when a bomb exploded on an outside ledge of Park Police Station in the Upper Haight neighborhood. See here. 
He would back up this correspondence with the 'Dragon Card' just one week later on April 28th 1970 declaring "I hope you enjoy yourselves when I have my blast." This card featured elements of the book Don Quixote, a novel by Miguel de Cervantes Saavedra, in which Alonso Quijana, a prolific reader of books, became so mesmerized by the chivalry contained within them, that under the assumed name of Don Quixote, along with his squire Sancho Panza, began a quest to revive this virtue. What the Zodiac Killer was inferring with this particular card can be debated, but the 1899 Waller Street Police Station is situated on the boundary of the San Francisco Golden Gate Park and in close proximity, also situated in the park, is the memorial statue of Miguel de Cervantes, featuring Don Quixote and Sancho Panza. Was the Zodiac Killer insinuating an attack close to the police station and park, similar to the murder of police officer Brian McDonnell.  

Then on June 26th 1970 this communication arrived, insinuating the murder of another police officer, Richard Radetich (25). On June 19th at 5.25 am he was gunned down by three shots from a .38 caliber revolver at point blank range through the driver side window of his vehicle, while in the process of serving a parking ticket by 643 Waller Street, San Francisco, in the Lower Haight District and subsequently died 15 hours later. The murder of Richard Radetich, as of writing, remains unsolved.
​The Zodiac Killer appeared to be heavily centering his focus in the Haight District. The statue in the park, 1899 Waller Street and 643 Waller Street all fall within a 2 mile radius, featured through three consecutive mailings.
It is therefore this locality of San Francisco we shall again turn our attention to, when considering where the Zodiac Killer may be directing his threat towards in the Button letter, using recent history to predict the future.
There is good reason to believe the Zodiac Killer was threatening an attack on Ingleside Station-San Francisco Police Department, located at 1 Sgt John V Young Lane, named in honor of Sgt. John Young, killed by gunmen in 1971 after they stormed the police station. Ingleside Station is 4.6 miles south of 1899 Waller Street. The Zodiac Killer never followed through on many of his claims, but this may very well be the location he was threatening to bomb on June 26th 1970. So here is the evidence.
When the Zodiac Killer mailed the Button letter, it was accompanied by a Phillips 66 road map and his crosshairs, stating they were "to be set to Mag.N." That is magnetic north, calculated at 17 degrees in 1970. Clearly he soon realized that the information or code he supplied, coupled with the Phillips 66 map, was insufficient to crack the cipher or determine a location for the bomb. One month later he rectified the problem with the Little List letter mailed on July 26th 1970, when he incorporated two further crosshairs, with all the clues we needed.     

This was the first crosshair on the right.
The Zodiac Killer continually taunted police with his running victim total, always attributing the police with zero. This was nothing new. However here he deliberately brings attention to the zero, marking it noticeably darker, as though it has increased significance. It is also placed within the crosshairs, indicating an area within his sights.
Bearing in mind the acronym SFPD, it is clear he has the San Francisco Police Department firmly focused as his target. That police department, we will attempt to show, was Ingleside Station located just off Balboa Park at San Jose Avenue.
The Zodiac Killer sent us a second set of crosshairs in the Little List letter stating "PS. The Mt Diablo code concerns Radians + inches along the radians."
This was the clue we needed.
In a previous article we highlighted a region of San Francisco for particular interest, using the following technique, but with improved map plotting and examining carefully the Phillips 66 map, it has become apparent the amended focus should be squarely over Ingleside Police Station.
The phrase "PS. The Mt Diablo code concerns Radians + inches along the radians," clearly tells us to use radians as our degrees from the north axis and is "to be set to Mag.N."  So we are looking for whole radians, to which we then add in the magnetic north value of 17 degrees. This will give us our angle on the Phillips 66 map.
The​ bold circle above is sitting between the 180 and 270 degree axis. In fact the center of the bold circle is positioned at 246 degrees. This can be confirmed using a compass rose. One radian is valued at 57.296 degrees, so four radians are valued at 4 X 57.296 = 229.184 degrees. Add in the magnetic north value of 17 degrees and our final total is 246.184 degrees.
The Zodiac Killer was indicating four radians + magnetic north. He never incorporated this into the Button letter code and Phillips 66 map, telling us the crosshair was to be set to magnetic north, but a month later in the Little List letter, he added the magnetic north value in for us, seen by the positioning of the bold circle next to SFPD. Four radians and 17 degrees is 246 degrees. This bold circle is also positioned at exactly 246 degrees (see below). 

This compass rose and SFPD crosshair, angled at 246 degrees can now be placed over the Phillips 66 map. But first we will examine the second  crosshair placed at the foot of the Little List letter.
The Zodiac Killer placed 'Diablo', the Spanish word for devil over the 180 degree axis. This may not have any significance, but if we couple the 66 from Phillips 66, with the number 6 on the Phillips map crosshair, we get 666, the number of the beast. By using the same method we can add the number 66 to the 180 degrees and arrive at 180 + 66 = 246 degrees once more.
Whether this was by design however, is open to question.
Let us now go ahead and superimpose the compass rose and SFPD crosshair over the Phillips 66 map (below).
To be completely accurate, both have been tilted by three degrees to match the original Zodiac crosshair. (shown here).
246 degrees takes us, as the crow flies, 31 miles southwest, passing directly over Ingleside Station-San Francisco Police Department (SFPD). The map scale is 6.4 miles to the inch, so if we were traveling inches along the radians, it would be 4.84 inches.  
If we round off, the phrase "PS. The Mt Diablo code concerns Radians + inches along the radians," would become: "PS. The Mt Diablo code concerns four Radians + five inches along the radians." That is 229 degrees, but set to magnetic north gives us the 246 degrees shown in the diagrams. 

The Button letter code however, as mentioned above, would not incorporate the exact angle or directions to Ingleside Station. Remember the Zodiac Killer stated "The Map coupled with this code will tell you where the bomb is set."
The map crosshair told us to "set to Mag. N", which was 17 degrees. So if the code had an angle within it, this angle would be 229 degrees (before it is coupled with the map).
With 29 unique characters in the 32 symbol code, simple substitution is not an option. Some form of key must be unearthed.
Below are two incorrect examples of what we may be looking for. The first example matches all the repeating characters, even the dotted circle, but makes no sense. The second is more recognizable as a logical sentence, but matches little within the code. You may have a better solution. 
Ingleside Police Station may very well have been the target of the Zodiac Killer, but without breaking the code, it will remain a possibility rather than a proven fact. Thank you for your time. 

In a recent article we examined the Mount Diablo code in conjunction with the Phillips 66 road map and suggested a possibility that the Zodiac 32 Symbol cipher may have revealed San Francisco International Airport, situated at 4 radians or 229 degrees from Mount Diablo. However,  coupled with the Magnetic North value of 17 degrees at the time of mailing, was to give us a final value of 246 degrees, exactly corresponding with the bold circle the Zodiac Killer provided within his crosshairs on the 'Little List' letter mailed on July 26th 1970.  View initial article (Part One). View Part Two.
This final part of the trilogy will attempt to cement the motivation behind the Zodiac Killer's crosshairs, which he gave us on the Phillips 66 road map (as part of the Button Letter) mailed on June 26th 1970 and the 'Little List' letter one month later on July 26th 1970. In the following diagram we have incorporated the three crosshairs together to better explain the findings. This idea has been covered before, but finalizes the three part story under one banner in a little more detail.

The Zodiac Killer stated on the Button letter "The Map coupled with this code will tell you where the bomb is set". In other words, the two are to be used in conjunction with each other. This is what we did in the earlier articles, taking the code of San Francisco International Airport at 229 degrees and coupling it with the map, set at a Magnetic North value of 17 degrees, to arrive at the final value of 246 degrees.
However, this would not have been possible using the Button letter and Phillips 66 road map alone. The Zodiac Killer realizing this, gave us the two additional crosshairs on the Little List Letter, with a couple more hints. Firstly, the bold circle and secondly the phrase "PS The Mt Diablo code concerns Radians + inches along the radians". The Zodiac Killer placed this phrase over the crosshairs itself, when he could have easily accommodated both elements separately - unless of course he had an ulterior motive.

The phrase "PS The Mt Diablo code concerns Radians + inches along the radians" runs over the south axis; or to be precise, over the 180 degree axis or number 6 on the Zodiac dial. The only word bisected by this south axis is​ Diablo. 
Let us expand upon the "Map coupled with this code will tell you where the bomb is set" to better explain things, using this phrase "The Phillips 66 Map coupled with this code will tell you where the bomb is set". In the first instance, the code of San Francisco International Airport or 229 degrees was coupled with the map set to Magnetic North of 17 degrees, to equal 246 degrees. The 'Mount Diablo code' was written on the 180 degree axis, so we will couple this 180 degrees with the map (or more specifically the Phillips 66 map), to give us 180 + 66 = 246 degrees, the exact position of the bold circle he provided us in the 'Little List' letter and exactly the same as 4 radians and 17 degrees. Then we shall take the number 6 he provided on the 180 degree axis and once again couple this with the Phillips 66 map to give us 666, the mark of the Devil or Diablo.

The conventional view is that the Mount Diablo peak derives its name from the 1805 escape of several Chupcan Native Americans from the Spanish in a nearby willow thicket. The natives seemed to disappear, and the Spanish soldiers thus gave the area the name "Monte del Diablo", meaning "thicket of the devil." Diablo was placed over the 180 degree mark and the number 6 axis, and on both occasions coupled with the 66 from the Phillips 66 road map, it gave us something significant. But whether or not this was his true intention is still unclear and may never be resolved. 

Footnote: What level of understanding the Zodiac Killer had regarding the concept of radians is unknown, but they are a counterclockwise value around the circumference of a circle. He placed his crosshairs over Mount Diablo, to which he added a sort of clock face, replacing the number twelve with a zero, stating it was "to be set to Mag.N". It can be shown that 4 radians and Magnetic North will fall within the bold, black circle he placed on his 'Little List' crosshairs. In addition, it can be shown that traveling 2 radians counterclockwise from True North will again fall within the bold, black circle. The use of the clock face and the directional north marker set at zero, may indicate that Zodiac intended this as his starting point for any calculations. The mere fact that the above measurements, either clockwise or counterclockwise, using whole radians, both fall inside the black circle, would seem to suggest that the 246 degree angle subtended from Mount Diablo over San Francisco is where we should be looking.​

In a recent article we examined the Mount Diablo code in conjunction with the Phillips 66 road map and suggested the possibility that the Zodiac 32 Symbol cipher may have revealed San Francisco International Airport, situated at 4 radians or 229 degrees from Mount Diablo. However, coupled with the Magnetic North value of 17 degrees at the time of mailing, it was to give us a final value of 246 degrees, exactly corresponding with the bold circle the Zodiac Killer subsequently provided within his crosshairs on the 'Little List' letter mailed on July 26th 1970. Here we will take this one step further and see where the adjustment of the Magnetic North value of 17 degrees takes us from the airport location and see if the pinpointed location makes any sense in respect to all we think we know about the Zodiac Killer. View initial article (Part One).  

It is difficult to be exact using the Zodiac diagrams, but the angle of 246 degrees passes over the Bayview-Hunters Point region of San Francisco, situated only 5.5 miles from the Mason and Geary intersection, where it is believed Paul Stine picked up the Zodiac Killer on October 11th 1969.
Passing through the Bayview area is 3rd Street, close to Highway 101, and two possible routes Paul Stine may have traveled on his return back from San Francisco International Airport after dropping off his final paying fare, before returning back to the San Francisco theater district. The Bayview-Hunters Point region has a colorful history and has courted much controversy and conflict down the years. 
​
After a San Francisco ordinance in 1868 banned the slaughter and processing of animals within the city proper, a group of butchers established a "butchers reservation" on 81-acre of tidal marshland in the Bayview district. Within ten years, 18 slaughterhouses were located in the area along with their associated production facilities for tanning, fertilizer, wool and tallow. The "reservation" (then bounded by present-day Ingalls Street, Third Street, from Islais Creek to Bayshore) and the surrounding houses and businesses became known as Butchertown. The butcher industry declined following the 1906 San Francisco earthquake until 1971 when the final slaughterhouse closed.
Taken from Wikipedia.
​
If we insert a Zodiac timeline to this, the final slaughterhouse closed in 1971, which is the year the Zodiac mailed us his second to last confirmed correspondence on March 13th 1971 to the Los Angeles Times, before he disappeared for close to three years, the irony of which cannot be ignored. Also from our experience, we have the suggestion that the Zodiac Killer may have served in the military, or had naval connections, a common theme in Zodiac circles. The Zodiac timeline is not a certain one, predominantly because of earlier murders that may or may not be attributed to him, such as the Riverside murder of Cheri Jo Bates on October 30th 1966, nevertheless, this is where we shall start.  

Is there anything that ties Riverside, Vallejo, Benicia and the Bayview-Hunters Point in San Francisco? We shall explore some options. The Long Beach Naval Shipyard, which closed in 1997, was located at Terminal Island between the city of Long Beach and the San Pedro district of Los Angeles and was situated approximately 23 miles south of the Los Angeles International Airport. It was a 1 hr 20 minutes drive west of Riverside. The Mare Island Naval Shipyard is located in Vallejo, the hot zone highlighted by geographic profiling pioneer, Kim Rossmo, who zoomed in on a possible home location of the Zodiac Killer. And finally, the Hunters-Point Naval Shipyard, San Francisco, located on 638 acres in the southeast corner of the city. 

​At the start of World War II the Navy recognized the need for greatly increased naval shipbuilding and repair facilities in the San Francisco Bay Area, and in 1940 acquired the property from the private owners, naming it Hunters Point Naval Shipyard. The property became one of the major shipyards of the west coast. It was later renamed Treasure Island Naval Station Hunters Point Annex. During the 1940's, many workers moved into the area to work at this shipyard and other wartime related industries.
The key fissile components of the first atomic bomb were loaded onto the USS Indianapolis in July 1945 at Hunters Point for transfer to Tinian. After World War II and until 1969, the Hunters Point shipyard was the site of the Naval Radiological Defense Laboratory, the US military's largest facility for applied nuclear research. The yard was used after the war to decontaminate ships from Operation Crossroads. Because of all the testing, there is widespread radiological contamination of the site. After the war, with an influx of blue collar industry, the area remained a naval base and commercial shipyard. The Navy operated the yard until 1974, when it leased most of it to a commercial ship repair company. Extract from Wikipedia. The Navy ceased operations in 1974, the year the Zodiac mailed his final confirmed letter, the Exorcist Letter on January 29th 1974. In fact, three further potential Zodiac letters were mailed that year, before the Zodiac Killer finally disappeared for good.

The Zodiac letters definitely switched emphasis after the Paul Stine murder on October 11th 1969, from the November 9th Bus Bomb letter through to the 'Little List' letter on July 26th 1970, making references to the murder of two San Francisco police officers, Brian McDonnell on February 16th 1970 and Sgt Richard Radetich on June 19th 1970. Bombing was definitely on the agenda, although it was believed he never followed up in any of his proposed threats. 

The question remains, was irony his intention, if he had indeed selected Hunters Point as a location, somewhere he may have been familiar with or even worked. Even the surrounding areas were once known as 'Butchertown'. It should be noted that a bombing did occur in the January of 1970 at Hunters Point Police Station, highlighted in this KPIX eyewitness report - and although with near certainty it was not the Zodiac Killer, it may have been something he was aware of, had he worked in this region of San Francisco.

Did the Zodiac Killer live and work in San Francisco during the majority of his crimes, placing distance between himself and the first three attacks, before coming home to roost, or did he live across the bay in the Vallejo/Benicia areas and only used San Francisco as a mailing point on his route to work?

The 246 degrees subtended from the center point of Mount Diablo runs directly across the Hunters-Point Naval Shipyard in the Bayview District, and was consolidated by the accuracy of the 'Little List' letter crosshairs. The Mare Island Naval Shipyard has always courted some attention in Zodiac circles, on account of the proposed naval connection to our killer. Did the Zodiac Killer work at both facilities, or even the third at Riverside. Was irony at work here, or is the Hunters-Point connection just simply wide of the mark once more. 

SEE PART THREE -  http://www.zodiacciphers.com/zodiac-news/sfi-airport-hunters-point-part-three

The Zodiac Killer after killing four people in Benicia, Vallejo and Napa, suddenly switched the emphasis to the heart of San Francisco, mailing a letter to the San Francisco Chronicle on October 13th 1969, promising to target a school bus and "pick of the kiddies as they come bouncing out". In the following months came multiple references to bombs, notably in his 'My Name is' letter, detailing a bus bomb diagram and suggesting he was not responsible for wiping out "that blue meannie with a bomb". He was describing the murder of San Francisco police officer Brian McDonnell on February 16th 1970, two months earlier, when a bomb packed with fence staples exploded on an outside ledge of Park Police Station in the Upper Haight neighborhood. The Zodiac Killer then mailed the Dragon card on April 28th 1970 stating "I hope you enjoy yourselves when I have my blast" and then the Button Letter on June 26th 1970, cementing his connection to San Francisco by part referencing the murder of a policeman in a parked car, thought to be Officer Richard Radetich outside 643 Waller Street. In this correspondence he attached a Phillips 66 road map of San Francisco and Vicinity, stating "the map coupled with this code will tell you where the bomb is set". Then on July 26th 1970 the 'Little List' letter was mailed, including two crosshairs, one with a prominent black circle including the acronym SFPD = 0 and the second referring us back to the Button letter, stating "The Mt Diablo code concerns radians + inches along the radians". The emphasis appeared squarely over the region of San Francisco, so was the bomb the Zodiac Killer promised us, to be found somewhere in this region.

What level of understanding the Zodiac Killer had regarding the concept of radians is unknown, but they are a counterclockwise value around the circumference of a circle. He placed his crosshairs over Mount Diablo, to which he added a sort of clock face, replacing the number twelve with a zero, stating it was "to be set to Mag.N". It can be shown that 4 radians and Magnetic North will fall within the bold, black circle he placed on his 'Little List' crosshairs. In addition, it can be shown that traveling 2 radians counterclockwise from True North will again fall within the bold, black circle. The use of the clock face and the directional north marker set at zero, may indicate that Zodiac intended this as his starting point for any calculations. The mere fact that the above measurements, either clockwise or counterclockwise, using whole radians, both fall inside the black circle, would seem to suggest that the 246 degree angle subtended from Mount Diablo over San Francisco is where we should be looking.

The Zodiac Killer referred to radians (an angle of measurement), of which one radian is valued at 57.296 degrees. If we look at the prominent black circle he gave us on the 'Little List' letter (shown on the right), its center falls over the 246 degree mark on a compass rose. 246 degrees is 4 radians + 17 degrees. When the Phillips 66 road map was mailed on June 26th 1970, Magnetic North was approximately 17 degrees. 

4 radians = 4 X 57.296 = 229.184 + 17 degrees = 246 degrees.
So, apparently the Zodiac Killer had some concept of radians and the value of Magnetic North, unless we are assuming he was just lucky in his placement of the bold circle on the diagram. His further reference to SFPD (San Francisco Police Department) next to this circle, suggests this is where we should be centering our focus, bearing in mind his disdain for law enforcement.
 
The Zodiac Killer wrote "The Mt Diablo code concerns radians + inches along the radians", so let us start with complete radians. We know from above calculations that the value of 4 radians (229 degrees) is significant, so we shall place a compass rose over Mount Diablo and see where this takes us, in respect of San Francisco. 

It can be seen that 229 degrees falls on the south edge of San Francisco International Airport by Old Bayshore Highway. 
Was the Zodiac Killer intending to ratchet up the fear by exploding bombs (or the threat of bombs) in the vicinity of the airport? This seems highly unlikely, so we shall take a further look at the Button letter mailed on June 26th 1970, where the Zodiac Killer stated "The Map coupled with this code will tell you where the bomb is set. You have until next Fall to dig it up" and enter something alongside the code.

San Francisco International Airport is comprised of exactly 32 letters and fits squarely alongside the 32 symbol Button letter code. However, the 246 degree mark falls further around the circumference of the compass rose. The 4 radians took us to San Francisco International Airport, but coupled with the map "to be set to Mag.N" gives us the final value of 246 degrees. The San Francisco International Airport may have been the clue but not the final destination, which should lie in the Hunters Point region or beyond.  

SEE PART TWO - http://www.zodiacciphers.com/zodiac-news/sfi-airport-part-two-hunters-point

Edward Edwards was a convicted serial killer who spent time at Old Montana State Prison and recollects in his autobiography 'Metamorphosis of a Criminal' memories from his time there, on this particular occasion another inmate, stating 'this man remains my most uncomfortable memory'. He goes on to say 'This demented individual showed an overwhelming interest in science fiction and Egyptian literature.' He also recollects that this individual believed that anyone he killed would become his slave in the next life. Whether or not this man was the Zodiac Killer is open to debate, but what we do know is that the Northern California killer appeared on the face of it to be immersed in history, often indicating in his literary correspondence and the symbolism contained within it, the ability to reference material that predated his existence, none more so than the Little List Letter, mailed to the San Francisco Chronicle on July 26th 1970. This lengthy correspondence paraphrased the Gilbert and Sullivan opera The Mikado, not once, but twice and backed this up with further reference in his Exorcist Letter, four years later when he pulled lines from Mikado Act 2, On a Tree by a River.
Using these above premises and the fact the Zodiac Killer tabled us his Little List on July 26th, it begged the question, did the murderer of innumerable people in the late 1960's and early 1970's, do so randomly when the compulsion desired or did he indeed stick rigidly to a plan, when he selected his victims, to be placed on his so called 'Little List'.
The next section is an expansion to the article 'The 13 Moon Calendar Crimes', exploring the idea that the Zodiac Killer did indeed have an agenda and one he remained loyal to, throughout his seemingly motiveless crimes. It became apparent that the Zodiac Killer selected his murders on nothing else but time, or to be more specific, by the date on a calendar. 
The Little List Letter was indicative of a killer, tired of the public, not seeing the whole picture, so within this correspondence he would give us at least four clues   

Firstly the reference to the Mikado, a two part comic opera by Gilbert and Sullivan, which opened for the public on March 14th 1885, and was hugely successful running for 672 performances at the Savoy Theatre in London. The key was in the date.
Secondly, was the reference to the number 13, and as one can see the thirteenth line of his recital implored us to see that his Little List 'are up in dates'.
Thirdly, was the date he mailed us his Little List Letter, July 26th, the most significant of all his clues.
Fourthly, 'As some day it must happen', along with a back reference from the 13 Hole Postcard 'The pace isn't any slower, in fact it's just one big thirteenth'.
All these clues are suggestive of a date specific element and would be found within the 13 Moon Calendar.
The 13 Moon Calendar was embedded in many ancient cultures, the star Sirius being integral to their beliefs. The heliacal rising of Sirius on July 26th, initiated the beginning of the Egyptian year and brought about the 1460 year Sothic cycle. The 13 Moon Calendar, consisting of a 13 month, 28 day cycle, was used by the Egyptian Thoth, Druids, Polynesians, Incas, along with some native Americans. The 13 Moon Calendar reflects this movement of Sirius and itself begins on July 26th, as opposed to our traditional Gregorian Calendar that begins the year on January 1st. Each month of 28 days is split into 4 weeks of 7 days and as such there are only four days per month that comprise a weeks beginning. That is day 1, 8, 15 and 22, shown here below left.
To view the 13 Moon Calendar and check the relevant dates in this article, open this page from the Law of Time website and scroll down the page to the large chart that begins with the Magnetic Moon. For example December 20th in the American system is written as 12/20. Keep this tab open.  http://www.lawoftime.org/thirteenmoon/tutorial.html

You will note that position 1, 8, 15 and 22 are all the first day of a calendar week.
Each month there are 28 days, so if the Zodiac Killer was selecting his victims randomly there would be an 85.7% chance they would not fall on the first day of the 13 Moon Calendar week, conversely if the Zodiac Killer was selecting his victims randomly there would only be a 4 in 28 chance or 14.3% chance they would be murdered on either day 1, 8, 15 or 22.
Of course it may be possible that one victim may fall on this date, but what are the odds for two, three or indeed thirteen. If they were murdered randomly then you would expect a random spread, but if the majority or all fell on the first day of the 13 Moon Calendar week, then that 14.3% chance becomes smaller and smaller with each victim, until the odds become that slim, you have to start believing that a correlation exists. The only other possibility is that miracles are a believable concept, however, it is not only the murders themselves we should consider, it is the Little List Letter itself.
The mailing of this letter was July 26th, which falls on the first day of the 13 Moon Calendar week and notably it is the beginning date of the 13 Moon Calendar also. The letter featured the Mikado which opened to the paying public on March 14th 1885 and March 14th also falls on the first day of the 13 Moon Calendar week. One letter, one list and two dates that fit into our criteria straight away, so lets move on. 
Two early crimes often linked to the Zodiac Killer were the murders of Robert Domingos and Linda Edwards on a remote Santa Barbara County beach on June 4th 1963 and the brutal stabbing of Cheri Jo Bates outside the Riverside City College Library on October 30th 1966, however neither of the crimes were specifically claimed by the Zodiac Killer, only a belated reference was made in the Los Angeles Letter mailed on March 13th 1971, when he stated 'I do have to give them credit for stumbling across my riverside activity', furthermore both of these crimes were committed in the pre-Zodiac era and neither date falls on the first day of the 13 Moon Calendar week, suggesting they were not the work of the Zodiac Killer, or were not committed under the Zodiac umbrella, however on December 20th 1968 things were about to change.   

The Lake Herman Road murders were the first confirmed attacks by the infamous Zodiac Killer, which he laid claim to on July 31st 1969, in three letters he mailed to authorities, that left us in no doubt we had a serial killer on our hands, indeed, claiming not only the murders of David Faraday and Betty Lou Jensen on December 20th 1968, but the murder and attempted murder of Darlene Ferrin and Michael Mageau at Blue Rock Springs Park in Vallejo on July 4th 1969. Even placing a phone call shortly after the second attack to police dispatcher Nancy Slover, to confirm the horror of that night's events and what would soon follow.
Both of these attacks and the three murders would now begin the infamous Little List the Zodiac Killer was compiling, as December 20th and July 4th would both fall on the first day of the 13 Moon Calendar week. Slim odds indeed, but this unfortunately was just the beginning. 
Almost three months later initial fears were well founded, when a masked assailant approached a courting couple on the shores of Lake Berryessa and after hogtying both Bryan Hartnell and Cecelia Shepard began his savage attack, stabbing the couple numerous times. Sadly Cecelia Shepard succumbed to her injuries two days later, but miraculously Bryan Hartnell survived and was able to recount the horror of that day from his hospital bedside. 
Even more miraculous was the date of the attack, September 27th 1969, another date that would just happen to fall on the first day of the 13 Moon Calendar week and our odds are getting slimmer. Curiously, even though all three attack dates fell on the first day of the week, they also all fell on position 8, possibly giving rise to the 888 on the 13 Symbol Cipher, but this is speculative at best.
Exactly two weeks later the Zodiac Killer changed course, when he took his murderous campaign across the bay to San Francisco, resulting in the callous assassination of taxi driver Paul Stine, discovered prostrate across the seat of his resting vehicle. The Zodiac Killer came into brief view for but a moment, witnessed by three teenagers from a house window across the street, but unfortunately he would make good his escape, exiting north along Cherry Street, an affluent neighborhood of Presidio Heights.

After this murder, the Zodiac Killer was never witnessed again, but by all accounts left his bloodied fingerprints, as testimony to a man that has subsequently become the most infamous killer in US history. But one further fingerprint was to be laid down, the date of his supposed final murder, October 11th 1969 and one more date that would fall on the first day of the 13 Moon Calendar week, indeed October 11th 1969 was a new moon, so from the perspective of the night sky, it could not have been darker, lending irony to a calendar date, that would yet again provide a significant ally to shield this killer as he dissolved into the shadows for one last time.
We now had four dates and four correlations, the odds are shortening, but don't believe for a minute that the coincidences stop there.
On November 8th 1969 his most infamous correspondence would land at the doorstep of the San Francisco Chronicle, another hidden clue would be contained within its envelope, in the form of a cipher, one that has remained unsolved to this day. However the number 888 may again have resurfaced within the code, to be found embedded within the name of Zodiac itself.
This concept is explored linking six or more correspondences of the Zodiac Killer together, including all his unsolved ciphers and can be viewed in the article 'The Three Unsolved Ciphers Linked'.
Not surprisingly, the date of November 8th fits our criteria and falls on the first day of the 13 Moon Calendar week.
The next correspondence to arrive was the Melvin Belli Letter on December 20th 1969, the anniversary of the Lake Herman Road double murder and that significant date once more. The letter itself states 'I am afraid I will loose control again and take my nineth + posibly tenth victom'. Considering the Zodiac Killer's history of attacking mainly couples, there was a distinct possibility his ninth and tenth victims may be a courting couple once more. So bearing in mind our 13 Moon Calendar, the next murders would likely fall on the first day of the calendar once again and the murders would show traits of the Zodiac Killer. We wouldn't have long to wait.
Two months later on February 21st 1970 John Franklin Hood (24), who had served decorated time in Vietnam in the 64th Armored Division and Sandra Garcia (20), who worked in the California Department of Motor Vehicles, decided to visit the quiet retreat of East Beach, Santa Barbara one evening, when they fell victim to a knife wielding assassin, not unlike the Lake Berryessa Attack on Bryan Hartnell and Cecelia Shepard and more crucially, unlike the murders of Robert Domingos and Linda Edwards, within the Zodiac timeline. February 21st falls on the first day of the 13 Moon Calendar week for the fifth attack in a row and all within the framework laid down within the Melvin Belli correspondence. The next letter to arrive on April 20th 1970 was the 13 Symbol Cipher and our worst fears would be realized, the Zodiac murder total had reached ten, indicating that two more victims had been placed on his list, the question being, were they John Franklin Hood and Sandra Garcia.
It can also be noted that on the 'My Name is....Cipher' letter, the Zodiac Killer wrote 'I have killed ten people to date', it is a matter of interpretation, he may possibly have killed ten people up to this point in time, but if these were his victims, he most certainly had killed 'ten people to date'. 

Next up was the abduction of Kathleen Johns, an account of which has always been heavily questioned. The date of the Modesto abduction was March 22nd 1970, superfluous in this case, as Kathleen Johns was not murdered. The Zodiac Killer had never showed any hesitation or leniency in any of his previous attacks, but if we are to believe this was our murderer, he appeared wholly indecisive, driving Kathleen Johns around for approximately two hours, whereas during his previous remote attacks, he presented his weapon and death was soon to follow. If we use his modus operandi as a guide and the date of March 22nd, which fails to fall on the first day of the 13 Moon Calendar, the two are compatible and lend weight to the hypothesis, that this crime was not the work of the Zodiac Killer. 
Along came another anniversary, that of July 4th 1970, exactly one year after the attack at Blue Rock Springs Park, but this night would again be no stranger to horror, when on another beach, this time in Santa Barbara, three men Thomas Victor Dolan (17), of Manhattan Beach, Thomas Hayes (19), of Hermosa Beach and Homer Clyde Shadwick (19), of Saginaw Michigan were brutally attacked with bladed instruments while they lay defenseless in their sleeping bags. Two of the victims succumbed to their injuries, while the third Thomas Hayes was rushed to hospital in nearby Goleta, in critical condition, but fortunately survived. Another anniversary, another relevant date, but sadly two more murders.
The Zodiac Killer may now have claimed nine victims in six different attacks, David Faraday December 20th 1968, Betty Lou Jensen December 20th 1968, Darlene Ferrin July 4th 1969, Cecelia Shepard September 27th 1969, Paul Stine October 11th 1969, John Hood February 21st 1970, Sandra Garcia February 21st 1970, Thomas Dolan July 4th 1970, Homer Shadwick July 4th 1970, all of which fall on the first day of the 13 Moon Calendar week.
A further two months later Donna Ann Lass disappeared, feared murdered after leaving the Sahara Tahoe Hotel, where she was employed as a nurse. Her case became entwined within the Zodiac sphere after the arrival of the Pines Card communication, suggesting a link to the Donna Lass case, however this was not the only reason, as her disappearance came just six months after the abduction and murder of another nurse Judith Hakari. She had been working at the Sutter Hospital in Sacramento on March 7th 1970 and later had pulled into the parking lot of the Markston Apartments, where she was likely abducted. One and a half months later she was discovered in a shallow grave, she had been beaten and strangled, but not sexually assaulted. Both the abduction and possible murder of both Hakari and Lass occurred on the first day of the week on the 13 Moon Calendar.         

Shortly after the disappearance of Donna Lass and two days prior to the Halloween Card, on October 25th 1970 Nancy Bennallack, a court reporter was found murdered, brutally stabbed numerous times in her own apartment. This, if indeed it was the Zodiac Killer would suggest a marked deviation from his previous crimes, however she was described as strikingly similar in appearance to Judith Hakari and was murdered just one block away.
October 25th falls yet again on the first day of the 13 Moon Calendar week. The Bermuda Triangle website describes these three murders as the Nightingale Murders, so for a more detailed connection and background to these cases, please visit bermuda-triangle.org/.
By the time the Halloween Card arrived the above murders would total 12 and the Halloween Card was suggesting that Paul Avery, a reporter at the San Francisco Chronicle may possibly become the Zodiac Killer's fourteenth victim. 
There is no suggestion that all these murders are the work of the Zodiac Killer, however they are the most commonly linked ones and most are credible possibilities, occurring within a relatively short time frame of 22 months. In other words 12 murders in 22 months, and all falling on the first day of the week on the 13 Moon Calendar. Three further victims, firstly, that of Robin Graham (18) who disappeared in the early hours of November 15th 1970 on the Hollywood Freeway after encountering car problems and noticed in the company of an unidentified dark haired male in possession of a pale Chevrolet Corvette. Secondly Jeanette Kamahele (20) on April 25th 1972 last spotted on Highway 101 Santa Rosa being aided by a white male driving a light brown Chevrolet pick up truck. And finally the strangled body of Lynn Maureen Derrick (24) found on a Sausalito side street on July 26th 1972, believed to have been murdered elsewhere and dumped, with the sound of a speeding car leaving the scene. These final three murders also fit the 13 Moon Calendar criteria and could push the final Zodiac total to 15, based upon date specifics. If Lynn Maureen Derrick was the Zodiac Killer's final victim it would be have not gone unnoticed that she was murdered on July 26th, the date the Little List was mailed to the San Francisco Chronicle and the beginning of the 13 Moon Calendar year, to mark, quite possibly the start of the end.    
What makes it even more striking, is that if you visit either the Zodiackiller.com forum or the Zodiackillersite forum, and select possible victims before the Lake Herman Road murders on December 20th 1968 and after the murder of Lynn Derrick on July 26th 1972, you will be hard pushed to find any murders that fall on the first day of the 13 Moon Calendar week, showing it is indeed a rare occurrence, but during this brief 22 months it occurs 12 times. If we include the disappearance of Robin Graham on November 15th 1970, this elevates to 13 in 23 months and would have come within one month of the Halloween Card seeking a fourteenth victim.
Coincidences rarely equate to facts, as many Zodiac suspects can testify to, but sometimes you just wonder.   

OPEN 13 MOON CALENDAR TO ENTER ALL DATES   

The final confirmed letter mailed by the infamous Zodiac Killer to the San Francisco Chronicle on January 29th 1974, has been commonly referred to as the Exorcist Letter. This sixty one word correspondence appeared to mock the 1973 movie 'The Exorcist', directed by William Friedkin and based on a novel by William Peter Blatty published in 1971, chronicling the demonic possession of a twelve year old girl, Regan MacNeil. William Peter Blatty spent long nights in a secluded Lake Tahoe cabin, crafting images of good and evil, religion, faith and the afterlife, that would eventually go on to make movie history and court its fair share of controversy along the way. 
The letter is short, reminiscent of much of the Zodiac Killer's later contact with authorities, but as well as mentioning the Exorcist movie, the letter, in rather disjointed fashion, breaks into a Mikado recital once again, recalling memories of the Little List Letter mailed three and a half years previously on July 26th 1970. But this time the foreboding 'Tit Willow' seemed contemplatory in this context, possibly marking the end of the Zodiac reign, and to this day, is still often quoted as the murderer's epitaph. The third and final section issued the usual threat of more murders, capped off with Asian style symbols, in the form of a cryptic message. 
Like much of his later correspondence there is little substance here, but we will attempt to delve a little deeper into the Exorcist letter and find any links that may be relevant or otherwise, as to why he wrote the letter in the first place. This is not a theory, just an examination into the reasoning, whereby the Zodiac Killer may have been drawing his inspiration.       

rabbit or hare, apparently gazing up at the wintry scene. One cannot help thinking the Zodiac Killer chose his cards for a reason.
Another interesting connection was noted on viewing the Tom Hanson Zodiac movie from 1971, in that the killer wore a Groucho Marx style nose and glasses in one scene from the movie. View the scene and thread at ZodiacKiller.com.
But this was not the only possible film connection to the Groucho Marx disguise featured on the 1990 Eureka Card.  

But can we connect Groucho Marx to the Exorcist Letter. Not directly, but by association.
The Zodiac Killer described The Exorcist as, "the best satirical comedy that I have ever seen". Well this may not be the case, however, the genesis of the movie may well have been born with the help of a comedy genius, that of Groucho Marx.
The Exorcist author William Peter Blatty was a close friend of Groucho Marx, indeed, there was an intention by Marx to dress as the priest Father Lankester Merrin from the movie and appear on the set of the Exorcist film, but due to scheduling matters, the comedic entrance never materialized. But in one episode of the popular 'You Bet Your Life' series, hosted by Groucho Marx, William Peter Blatty was a contestant and walked away with a prize of $10,000. When he was asked what he was going to do with the money, he stated he was to take some time off  to work on a novel. That novel was the acclaimed forerunner to the movie 'The Exorcist'. 

All that is left to do now is examine the strange symbol at the foot of the Exorcist Letter, but we will leave that for another time.

Waiting in the wings, the Zodiac Killer was not content with a supporting role and yearned to have his name in the spotlight, determined to act out his deep seated desire on a much grander scale - but unlike the theatrical tragedies that had gone before him, this one was to be performed on the very real stage of Northern California, with dark consequences. This analysis probes into the mindset of the Zodiac Killer and his influences as the driving force behind the numerous communications he orchestrated over a period of nearly five years, to narrow down a profession that, above all, takes center stage. It has been noted on countless occasions that the Zodiac Killer had leanings toward the dramatic, His early correspondence included part inference to The Most Dangerous Game, a short story by Richard Connell, published on January 19th 1924, as well as several references to the Gilbert and Sullivan comic opera, The Mikado, first viewed by the paying public on March 14th 1885. The Mikado featured heavily in his 'Little List' letter, mailed to the San Francisco Chronicle on July 26th 1970 and was resurrected in the 'Exorcist' letter, his last confirmed correspondence, mailed on January 29th 1974.

In the counterculture revolution of the 1960s, a new breed of expressionism emerged, in alliance with the already existing forces of cinema and theater that permeated the San Francisco culture and provided the backdrop for a diverse cocktail of literary and visual freedom.​

He claimed in his Bus Bomb letter of November 9th 1969 "The police shall never catch me, because I have been too clever for them.  I look like the description passed out only when I do my thing, the rest of the time I look entirle different. I shall not tell you what my descise consists of when I kill". He also made a grand appearance at Lake Berryessa on September 27th 1969, having purchased, borrowed or crafted a black executioner's hood and a waistline bib, emblazoned with the Zodiac crosshairs - but either way, his entrance was of theatrical proportions.

One thing evident throughout his correspondence, was his use of the word shall, leading to speculation that he may have been of British origin, as the word shall, is infrequently used in American English. However, another option exists. As a member of theater production, his exposure to the word shall would have been far more frequent in the performance of stage plays, particularly in traditional works of English origin, which he would seek to take to the next level when he started crafting his own scripts. Embittered by rejection, he mailed his work to the heart of the American people via the San Francisco Chronicle, seeking literary recognition, but sadly only succeeded in creating a tragedy of epic proportions, while hiding behind a pseudonym and mask of sanity.

The Button letter was mailed on June 26th 1970 containing a footnote that stated "The map coupled with this code will tell you where the bomb is set. You have until next fall to dig it up". No bomb or any other relevant location was subsequently discovered. The Zodiac Killer's November 8th 1969 340 cipher remained "crackproof", the April 20th 1970 '13 Symbol' cipher was simply too short for any meaningful decryption, and by late July of 1970, this new '32 symbol' code and 'Phillips 66 Road Map' mailed on June 26th 1970 failed to provide little relief for an audience on the wane.